提交 05002b87 编写于 作者: T Tao Luo 提交者: GitHub

Merge pull request #51 from luotao1/bug

bug fix
......@@ -11,7 +11,7 @@
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431Q480 431 488 421T496 402L420 84Q419 79 419 68Q419 43 426 35T447 26Q469 29 482 57T512 145Q514 153 532 153Q551 153 551 144Q550 139 549 130T540 98T523 55T498 17T462 -8Q454 -10 438 -10Q372 -10 347 46Q345 45 336 36T318 21T296 6T267 -6T233 -11Q189 -11 155 7Q103 38 103 113Q103 170 138 262T173 379Q173 380 173 381Q173 390 173 393T169 400T158 404H154Q131 404 112 385T82 344T65 302T57 280Q55 278 41 278H27Q21 284 21 287Z"></path></defs></svg></div><div id="wmd-preview" class="wmd-preview wmd-preview-full-reader"><div class="md-section-divider"></div><div class="md-section-divider"></div><h1 data-anchor-id="woa1" id="情感分析">情感分析</h1><div class="md-section-divider"></div><h2 data-anchor-id="6sb6" id="背景介绍">背景介绍</h2><p data-anchor-id="p24n">在自然语言处理中,情感分析一般是指判断一段文本所表达的情绪状态。其中,一段文本可以是一个句子,一个段落或一个文档。情绪状态可以是两类,如(正面,负面),(高兴,悲伤);也可以是三类,如(积极,消极,中性)等等。情感分析的应用场景十分广泛,如把用户在购物网站(亚马逊、天猫、淘宝等)、旅游网站、电影评论网站上发表的评论分成正面评论和负面评论;或为了分析用户对于某一产品的整体使用感受,抓取产品的用户评论并进行情感分析等等。表格1展示了对电影评论进行情感分析的例子:</p><table data-anchor-id="ydgg" class="table table-striped-white table-bordered">
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stroke-width="1" d="M21 287Q21 295 30 318T55 370T99 420T158 442Q204 442 227 417T250 358Q250 340 216 246T182 105Q182 62 196 45T238 27T291 44T328 78L339 95Q341 99 377 247Q407 367 413 387T427 416Q444 431 463 431Q480 431 488 421T496 402L420 84Q419 79 419 68Q419 43 426 35T447 26Q469 29 482 57T512 145Q514 153 532 153Q551 153 551 144Q550 139 549 130T540 98T523 55T498 17T462 -8Q454 -10 438 -10Q372 -10 347 46Q345 45 336 36T318 21T296 6T267 -6T233 -11Q189 -11 155 7Q103 38 103 113Q103 170 138 262T173 379Q173 380 173 381Q173 390 173 393T169 400T158 404H154Q131 404 112 385T82 344T65 302T57 280Q55 278 41 278H27Q21 284 21 287Z"></path></defs></svg></div><div id="wmd-preview" class="wmd-preview wmd-preview-full-reader"><div class="md-section-divider"></div><div class="md-section-divider"></div><h1 data-anchor-id="woa1" id="情感分析">情感分析</h1><div class="md-section-divider"></div><h2 data-anchor-id="6sb6" id="背景介绍">背景介绍</h2><p data-anchor-id="p24n">在自然语言处理中,情感分析一般是指判断一段文本所表达的情绪状态。其中,一段文本可以是一个句子,一个段落或一个文档。情绪状态可以是两类,如(正面,负面),(高兴,悲伤);也可以是三类,如(积极,消极,中性)等等。情感分析的应用场景十分广泛,如把用户在购物网站(亚马逊、天猫、淘宝等)、旅游网站、电影评论网站上发表的评论分成正面评论和负面评论;或为了分析用户对于某一产品的整体使用感受,抓取产品的用户评论并进行情感分析等等。表格1展示了对电影评论进行情感分析的例子:</p><table data-anchor-id="ydgg" class="table table-striped-white table-bordered">
<thead>
<tr>
<th>电影评论</th>
......@@ -34,20 +34,20 @@
<td>剧情四星。但是圆镜视角加上婺源的风景整个非常有中国写意山水画的感觉,看得实在太舒服了。。</td>
<td>正面</td>
</tr>
</tbody></table><p align="center" data-anchor-id="zxk7">表格 1 电影评论情感分析</p><div class="md-section-divider"></div><div class="md-section-divider"></div><p align="center" data-anchor-id="jos4">
</tbody></table><p data-anchor-id="vben">在自然语言处理中,情感分析属于典型的<strong>文本分类</strong>问题,即把需要进行情感分析的文本划分为其所属类别。文本分类涉及文本表示和分类方法两个问题。在深度学习的方法出现之前,主流的文本表示方法为词袋模型BOW(bag of words),话题模型等等;分类方法有SVM(support vector machine), LR(logistic regression)等等。 </p><p data-anchor-id="g3bc">对于一段文本,BOW表示会忽略其词顺序、语法和句法,将这段文本仅仅看做是一个词集合,因此BOW方法并不能充分表示文本的语义信息。例如,句子“这部电影糟糕透了”和“一个乏味,空洞,没有内涵的作品”在情感分析中具有很高的语义相似度,但是它们的BOW表示的相似度为0。又如,句子“一个空洞,没有内涵的作品”和“一个不空洞而且有内涵的作品”的BOW相似度很高,但实际上它们的意思很不一样。 </p><p data-anchor-id="9b8i">本章我们所要介绍的深度学习模型克服了BOW表示的上述缺陷,它在考虑词顺序的基础上把文本映射到低维度的语义空间,并且以端对端(end to end)的方式进行文本表示及分类,其性能相对于传统方法有显著的提升[<a href="#参考文献">1</a>]。</p><div class="md-section-divider"></div><h2 data-anchor-id="o6dd" id="模型概览">模型概览</h2><p data-anchor-id="pfp7">本章所使用的文本表示模型为卷积神经网络(Convolutional Neural Networks)和循环神经网络(Recurrent Neural Networks)及其扩展。下面依次介绍这几个模型。</p><div class="md-section-divider"></div><h3 data-anchor-id="3ho4" id="文本卷积神经网络cnn">文本卷积神经网络(CNN)</h3><p data-anchor-id="tb0x">卷积神经网络经常用来处理具有类似网格拓扑结构(grid-like topology)的数据。例如,图像可以视为二维网格的像素点,自然语言可以视为一维的词序列。卷积神经网络可以提取多种局部特征,并对其进行组合抽象得到更高级的特征表示。实验表明,卷积神经网络能高效地对图像及文本问题进行建模处理。 </p><p data-anchor-id="3mtf">卷积神经网络主要由卷积(convolution)和池化(pooling)操作构成,其应用及组合方式灵活多变,种类繁多。本小结我们以一种简单的文本分类卷积神经网络为例进行讲解[<a href="#参考文献">1</a>],如图1所示:</p><p align="center" data-anchor-id="jos4">
<img src="https://raw.githubusercontent.com/PaddlePaddle/book/develop/understand_sentiment/image/text_cnn.png" width="700"><br>
图1. 卷积神经网络文本分类模型
</p><p data-anchor-id="514w">假设待处理句子的长度为<span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-1-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -464.0516853480245 600.5 496.10337069604896" style="width: 1.39ex; height: 1.158ex; vertical-align: -0.116ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-6E"></use></g></svg></span><script type="math/tex" id="MathJax-Element-1">n</script>,其中第<span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-2-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -682.0516853480245 345.5 714.103370696049" style="width: 0.811ex; height: 1.622ex; vertical-align: -0.116ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-69"></use></g></svg></span><script type="math/tex" id="MathJax-Element-2">i</script>个词的词向量(word embedding)为<span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-3-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -922.4713132022996 3331.117134844292 1101.0082799245627" style="width: 7.761ex; height: 2.548ex; vertical-align: -0.463ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-78"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-69" x="809" y="-213"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-2208" x="1194" y="0"></use><g transform="translate(2139,0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJAMS-52"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-6B" x="1021" y="581"></use></g></g></svg></span><script type="math/tex" id="MathJax-Element-3">x_i\in\mathbb{R}^k</script><span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-4-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -715.0516853480245 521.5 747.103370696049" style="width: 1.158ex; height: 1.737ex; vertical-align: -0.116ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-6B"></use></g></svg></span><script type="math/tex" id="MathJax-Element-4">k</script>为维度大小。 </p><p data-anchor-id="gvwb">首先,进行词向量的拼接操作:将每<span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-5-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -715.0516853480245 576.5 747.103370696049" style="width: 1.39ex; height: 1.737ex; vertical-align: -0.116ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-68"></use></g></svg></span><script type="math/tex" id="MathJax-Element-5">h</script>个词拼接起来形成一个大小为<span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-6-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -715.0516853480245 576.5 747.103370696049" style="width: 1.39ex; height: 1.737ex; vertical-align: -0.116ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-68"></use></g></svg></span><script type="math/tex" id="MathJax-Element-6">h</script>的词窗口,记为<span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-7-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -463.0516853480245 3220.5592860057245 691.7932335345324" style="width: 7.529ex; height: 1.622ex; vertical-align: -0.579ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-78"></use><g transform="translate(572,-150)"><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-69"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-3A" x="345" y="0"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-69" x="624" y="0"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-2B" x="969" y="0"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-68" x="1747" y="0"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-2212" x="2324" y="0"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-31" x="3103" y="0"></use></g></g></svg></span><script type="math/tex" id="MathJax-Element-7">x_{i:i+h-1}</script>,它表示词序列<span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-8-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -463.0516853480245 8191.991680149484 691.7932335345324" style="width: 18.996ex; height: 1.622ex; vertical-align: -0.579ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-78"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-69" x="809" y="-213"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-2C" x="916" y="0"></use><g transform="translate(1361,0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-78"></use><g transform="translate(572,-150)"><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-69"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-2B" x="345" y="0"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-31" x="1124" y="0"></use></g></g><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-2C" x="3183" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-2026" x="3628" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-2C" x="4967" y="0"></use><g transform="translate(5412,0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-78"></use><g transform="translate(572,-150)"><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-69"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-2B" x="345" y="0"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-68" x="1124" y="0"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-2212" x="1700" y="0"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-31" x="2479" y="0"></use></g></g></g></svg></span><script type="math/tex" id="MathJax-Element-8">x_{i},x_{i+1},\ldots,x_{i+h-1}</script>的拼接,其中,<span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-9-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -682.0516853480245 345.5 714.103370696049" style="width: 0.811ex; height: 1.622ex; vertical-align: -0.116ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-69"></use></g></svg></span><script type="math/tex" id="MathJax-Element-9">i</script>表示词窗口中第一个词在整个句子中的位置,取值范围从<span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-10-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -687.0516853480245 500.5 708.103370696049" style="width: 1.158ex; height: 1.622ex; vertical-align: -0.116ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-31"></use></g></svg></span><script type="math/tex" id="MathJax-Element-10">1</script><span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-11-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -715.0516853480245 4123.388888888889 818.103370696049" style="width: 9.614ex; height: 1.853ex; vertical-align: -0.347ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-6E"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-2212" x="822" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-68" x="1823" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-2B" x="2622" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-31" x="3622" y="0"></use></g></svg></span><script type="math/tex" id="MathJax-Element-11">n-h+1</script><span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-12-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -922.4713132022996 6042.518087304109 1151.2128613888076" style="width: 14.015ex; height: 2.664ex; vertical-align: -0.579ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-78"></use><g transform="translate(572,-150)"><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-69"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-3A" x="345" y="0"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-69" x="624" y="0"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-2B" x="969" y="0"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-68" x="1747" y="0"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-2212" x="2324" y="0"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-31" x="3103" y="0"></use></g><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-2208" x="3498" y="0"></use><g transform="translate(4443,0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJAMS-52"></use><g transform="translate(722,410)"><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-68"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-6B" x="576" y="0"></use></g></g></g></svg></span><script type="math/tex" id="MathJax-Element-12">x_{i:i+h-1}\in\mathbb{R}^{hk}</script></p><p data-anchor-id="6eru">其次,进行卷积操作:把卷积核(kernel)<span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-13-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -922.4713132022996 3538.458801298385 984.522998550324" style="width: 8.224ex; height: 2.317ex; vertical-align: -0.232ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-77"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-2208" x="994" y="0"></use><g transform="translate(1939,0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJAMS-52"></use><g transform="translate(722,410)"><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-68"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-6B" x="576" y="0"></use></g></g></g></svg></span><script type="math/tex" id="MathJax-Element-13">w\in\mathbb{R}^{hk}</script>应用于包含<span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-14-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -715.0516853480245 576.5 747.103370696049" style="width: 1.39ex; height: 1.737ex; vertical-align: -0.116ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-68"></use></g></svg></span><script type="math/tex" id="MathJax-Element-14">h</script>个词的窗口<span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-15-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -463.0516853480245 3220.5592860057245 691.7932335345324" style="width: 7.529ex; height: 1.622ex; vertical-align: -0.579ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-78"></use><g transform="translate(572,-150)"><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-69"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-3A" x="345" y="0"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-69" x="624" y="0"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-2B" x="969" y="0"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-68" x="1747" y="0"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-2212" x="2324" y="0"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-31" x="3103" y="0"></use></g></g></svg></span><script type="math/tex" id="MathJax-Element-15">x_{i:i+h-1}</script>,得到特征<span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-16-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -771.0516853480245 9753.809123350122 1042.103370696049" style="width: 22.703ex; height: 2.432ex; vertical-align: -0.695ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-63"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-69" x="613" y="-213"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-3D" x="1055" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-66" x="2111" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-28" x="2662" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-77" x="3051" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-22C5" x="3990" y="0"></use><g transform="translate(4491,0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-78"></use><g transform="translate(572,-150)"><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-69"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-3A" x="345" y="0"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-69" x="624" y="0"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-2B" x="969" y="0"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-68" x="1747" y="0"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-2212" x="2324" y="0"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-31" x="3103" y="0"></use></g></g><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-2B" x="7934" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-62" x="8934" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-29" x="9364" y="0"></use></g></svg></span><script type="math/tex" id="MathJax-Element-16">c_i=f(w\cdot x_{i:i+h-1}+b)</script>,其中<span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-17-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -715.0516853480245 2375.0555555555557 777.103370696049" style="width: 5.56ex; height: 1.853ex; vertical-align: -0.232ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-62"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-2208" x="707" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJAMS-52" x="1652" y="0"></use></g></svg></span><script type="math/tex" id="MathJax-Element-17">b\in\mathbb{R}</script>为偏置项(bias),<span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-18-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -726.0516853480245 550.5 952.103370696049" style="width: 1.274ex; height: 2.201ex; vertical-align: -0.579ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-66"></use></g></svg></span><script type="math/tex" id="MathJax-Element-18">f</script>为非线性激活函数,如<span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-19-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -715.0516853480245 3528.5 941.103370696049" style="width: 8.224ex; height: 2.201ex; vertical-align: -0.579ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-73"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-69" x="469" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-67" x="815" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-6D" x="1295" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-6F" x="2174" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-69" x="2659" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-64" x="3005" y="0"></use></g></svg></span><script type="math/tex" id="MathJax-Element-19">sigmoid</script>。将卷积核应用于句子中所有的词窗口<span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-20-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; 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mode=display" id="MathJax-Element-21">c=[c_1,c_2,\ldots,c_{n-h+1}], c \in \mathbb{R}^{n-h+1}</script></p><p data-anchor-id="vkpd">接下来,对特征图采用时间维度上的最大池化(max pooling over time)操作得到此卷积核对应的整句话的特征<span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-22-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -702.8583648847041 556.1 735.9100502327285" style="width: 1.274ex; height: 1.737ex; vertical-align: -0.116ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-63" x="33" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-5E" x="55" y="-13"></use></g></svg></span><script type="math/tex" id="MathJax-Element-22">\hat c</script>,它是特征图中所有元素的最大值:</p><div class="md-section-divider"></div><p data-anchor-id="od9l"><span class="MathJax_Preview"></span><div class="MathJax_SVG_Display" role="textbox" aria-readonly="true" style="text-align: center;"><span class="MathJax_SVG" id="MathJax-Element-23-Frame" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -771.0516853480245 5083.155555555555 1042.103370696049" style="width: 11.815ex; height: 2.432ex; vertical-align: -0.695ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-63" x="33" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-5E" x="55" y="-13"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-3D" x="833" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-6D" x="1890" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-61" x="2768" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-78" x="3298" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-28" x="3870" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-63" x="4260" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-29" x="4693" y="0"></use></g></svg></span></div><script type="math/tex; mode=display" id="MathJax-Element-23">\hat c=max(c)</script></p><p data-anchor-id="tmo2">在实际应用中,我们会使用多个卷积核来处理句子,窗口大小相同的卷积核堆叠起来形成一个矩阵(上文中的单个卷积核参数<span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-24-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -464.0516853480245 716.5 496.10337069604896" style="width: 1.622ex; height: 1.158ex; vertical-align: -0.116ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-77"></use></g></svg></span><script type="math/tex" id="MathJax-Element-24">w</script>相当于矩阵的某一行),这样可以更高效的完成运算。另外,我们也可使用窗口大小不同的卷积核来处理句子(图1作为示意画了四个卷积核,不同颜色表示不同大小的卷积核操作)。 </p><p data-anchor-id="pbpk">最后,将所有卷积核得到的特征拼接起来即为文本的定长向量表示,对于文本分类问题,将其连接至softmax即构建出完整的模型。</p><p data-anchor-id="5gyc">对于一般的短文本分类问题,上文所述的简单的文本卷积网络即可达到很高的正确率[<a href="#参考文献">1</a>]。若想得到更抽象更高级的文本特征表示,可以构建深层文本卷积神经网络[<a href="#参考文献">2</a>,<a href="#参考文献">3</a>]。</p><div class="md-section-divider"></div><h3 data-anchor-id="76da" id="循环神经网络rnn">循环神经网络(RNN)</h3><p data-anchor-id="jix2">循环神经网络是一种能对序列数据进行精确建模的有力工具。实际上,循环神经网络的理论计算能力是图灵完备的[<a href="#参考文献">4</a>]。自然语言是一种典型的序列数据(词序列),近年来,循环神经网络及其变体(如long short term memory[<a href="#参考文献">5</a>]等)在自然语言处理的多个领域,如语言模型、句法解析、语义角色标注(或一般的序列标注)、语义表示、图文生成、对话、机器翻译等任务上均表现优异甚至成为目前效果最好的方法。</p><p align="center" data-anchor-id="5qsd">
<img src="https://raw.githubusercontent.com/PaddlePaddle/book/develop/understand_sentiment/image/rnn.png" width="400"><br>
图2. 循环神经网络按时间展开的示意图
</p><p data-anchor-id="rwui">循环神经网络按时间展开后如图2所示:在第<span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-25-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -647.0516853480245 361.5 679.103370696049" style="width: 0.811ex; height: 1.622ex; vertical-align: -0.116ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-74"></use></g></svg></span><script type="math/tex" id="MathJax-Element-25">t</script>时刻,网络读入第<span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-26-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -647.0516853480245 361.5 679.103370696049" style="width: 0.811ex; height: 1.622ex; vertical-align: -0.116ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-74"></use></g></svg></span><script type="math/tex" id="MathJax-Element-26">t</script>个输入<span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-27-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -463.0516853480245 928.1191013989369 641.5886520702876" style="width: 2.201ex; height: 1.506ex; vertical-align: -0.463ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-78"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-74" x="809" y="-213"></use></g></svg></span><script type="math/tex" id="MathJax-Element-27">x_t</script>(向量表示)及前一时刻隐层的状态值<span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-28-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -715.0516853480245 1836.5086745365313 893.5886520702876" style="width: 4.286ex; height: 2.085ex; vertical-align: -0.463ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-68"></use><g transform="translate(576,-150)"><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-74"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-2212" x="361" y="0"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-31" x="1140" y="0"></use></g></g></svg></span><script type="math/tex" id="MathJax-Element-28">h_{t-1}</script>(向量表示,<span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-29-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -715.0516853480245 1030.406943983867 901.3668266633396" style="width: 2.432ex; height: 2.085ex; vertical-align: -0.579ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-68"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-30" x="815" y="-213"></use></g></svg></span><script type="math/tex" id="MathJax-Element-29">h_0</script>一般初始化为<span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-30-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -687.0516853480245 500.5 730.103370696049" style="width: 1.158ex; height: 1.737ex; vertical-align: -0.232ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-30"></use></g></svg></span><script type="math/tex" id="MathJax-Element-30">0</script>向量),计算得出本时刻隐层的状态值<span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-31-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -715.0516853480245 932.1191013989369 893.5886520702876" style="width: 2.201ex; height: 2.085ex; vertical-align: -0.463ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-68"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-74" x="815" y="-213"></use></g></svg></span><script type="math/tex" id="MathJax-Element-31">h_t</script>,重复这一步骤直至读完所有输入。如果将循环神经网络所表示的函数记为<span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-32-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -726.0516853480245 550.5 952.103370696049" style="width: 1.274ex; height: 2.201ex; vertical-align: -0.579ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-66"></use></g></svg></span><script type="math/tex" id="MathJax-Element-32">f</script>,则其公式可表示为:</p><div class="md-section-divider"></div><p data-anchor-id="ffs1"><span class="MathJax_Preview"></span><div class="MathJax_SVG_Display" role="textbox" aria-readonly="true" style="text-align: center;"><span class="MathJax_SVG" id="MathJax-Element-33-Frame" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -771.0516853480245 19507.476147537123 1042.103370696049" style="width: 45.29ex; height: 2.432ex; vertical-align: -0.695ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-68"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-74" x="815" y="-213"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-3D" x="1209" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-66" x="2266" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-28" x="2816" y="0"></use><g transform="translate(3206,0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-78"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-74" x="809" y="-213"></use></g><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-2C" x="4134" y="0"></use><g transform="translate(4579,0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-68"></use><g transform="translate(576,-150)"><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-74"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-2212" x="361" y="0"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-31" x="1140" y="0"></use></g></g><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-29" x="6415" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-3D" x="7083" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-3C3" x="8139" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-28" x="8712" y="0"></use><g transform="translate(9101,0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-57"></use><g transform="translate(944,-150)"><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-78"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-68" x="572" y="0"></use></g></g><g transform="translate(10958,0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-78"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-74" x="809" y="-213"></use></g><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-2B" x="12108" y="0"></use><g transform="translate(13109,0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-57"></use><g transform="translate(944,-150)"><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-68"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-68" x="576" y="0"></use></g></g><g transform="translate(14969,0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-68"></use><g transform="translate(576,-150)"><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-68"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-2212" x="576" y="0"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-31" x="1355" y="0"></use></g></g><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-2B" x="17180" y="0"></use><g transform="translate(18180,0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-62"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-68" x="607" y="-213"></use></g><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-29" x="19117" y="0"></use></g></svg></span></div><script type="math/tex; mode=display" id="MathJax-Element-33">h_t=f(x_t,h_{t-1})=\sigma(W_{xh}x_t+W_{hh}h_{h-1}+b_h)</script></p><p data-anchor-id="863e">其中<span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-34-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -704.0516853480245 1856.9656915833432 882.5886520702876" style="width: 4.286ex; height: 2.085ex; vertical-align: -0.463ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-57"></use><g transform="translate(944,-150)"><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-78"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-68" x="572" y="0"></use></g></g></svg></span><script type="math/tex" id="MathJax-Element-34">W_{xh}</script>是输入到隐层的矩阵参数,<span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-35-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -704.0516853480245 1859.7941187080894 882.5886520702876" style="width: 4.286ex; height: 2.085ex; vertical-align: -0.463ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-57"></use><g transform="translate(944,-150)"><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-68"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-68" x="576" y="0"></use></g></g></svg></span><script type="math/tex" id="MathJax-Element-35">W_{hh}</script>是隐层到隐层的矩阵参数,<span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-36-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -715.0516853480245 937.1470593540447 893.5886520702876" style="width: 2.201ex; height: 2.085ex; vertical-align: -0.463ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-62"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-68" x="607" y="-213"></use></g></svg></span><script type="math/tex" id="MathJax-Element-36">b_h</script>为隐层的偏置向量(bias)参数,<span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-37-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -452.0516853480245 572.5 484.10337069604896" style="width: 1.274ex; height: 1.158ex; vertical-align: -0.116ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-3C3"></use></g></svg></span><script type="math/tex" id="MathJax-Element-37">\sigma</script><span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-38-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -715.0516853480245 3528.5 941.103370696049" style="width: 8.224ex; height: 2.201ex; vertical-align: -0.579ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-73"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-69" x="469" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-67" x="815" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-6D" x="1295" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-6F" x="2174" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-69" x="2659" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-64" x="3005" y="0"></use></g></svg></span><script type="math/tex" id="MathJax-Element-38">sigmoid</script>函数。 </p><p data-anchor-id="7ac9">在处理自然语言时,一般会先将词(one-hot表示)映射为其词向量(word embedding)表示,然后再作为循环神经网络每一时刻的输入<span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-39-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -463.0516853480245 928.1191013989369 641.5886520702876" style="width: 2.201ex; height: 1.506ex; vertical-align: -0.463ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-78"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-74" x="809" y="-213"></use></g></svg></span><script type="math/tex" id="MathJax-Element-39">x_t</script>。此外,可以根据实际需要的不同在循环神经网络的隐层上连接其它层。如,可以把一个循环神经网络的隐层输出连接至下一个循环神经网络的输入构建深层(deep or stacked)循环神经网络,或者提取最后一个时刻的隐层状态作为句子表示进而使用分类模型等等。 </p><div class="md-section-divider"></div><h3 data-anchor-id="opm4" id="长短期记忆网络lstm">长短期记忆网络(LSTM)</h3><p data-anchor-id="puym">对于较长的序列数据,循环神经网络的训练过程中容易出现梯度消失或爆炸现象[<a href="#参考文献">6</a>]。为了解决这一问题,Hochreiter S, Schmidhuber J. (1997)提出了LSTM(long short term memory[<a href="#参考文献">5</a>])。 </p><p data-anchor-id="ornj">相比于简单的循环神经网络,LSTM增加了记忆单元<span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-40-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -463.0516853480245 433.5 496.10337069604896" style="width: 1.042ex; height: 1.158ex; vertical-align: -0.116ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-63"></use></g></svg></span><script type="math/tex" id="MathJax-Element-40">c</script>、输入门<span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-41-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -682.0516853480245 345.5 714.103370696049" style="width: 0.811ex; height: 1.622ex; vertical-align: -0.116ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-69"></use></g></svg></span><script type="math/tex" id="MathJax-Element-41">i</script>、遗忘门<span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-42-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -726.0516853480245 550.5 952.103370696049" style="width: 1.274ex; height: 2.201ex; vertical-align: -0.579ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-66"></use></g></svg></span><script type="math/tex" id="MathJax-Element-42">f</script>及输出门<span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-43-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -462.0516853480245 485.5 494.10337069604896" style="width: 1.158ex; height: 1.158ex; vertical-align: -0.116ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-6F"></use></g></svg></span><script type="math/tex" id="MathJax-Element-43">o</script>。这些门及记忆单元组合起来大大提升了循环神经网络处理长序列数据的能力。若将基于LSTM的循环神经网络表示的函数记为<span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-44-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -701.0516853480245 749.5 722.103370696049" style="width: 1.737ex; height: 1.622ex; vertical-align: -0.116ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-46"></use></g></svg></span><script type="math/tex" id="MathJax-Element-44">F</script>,则其公式为:</p><div class="md-section-divider"></div><p data-anchor-id="5cdo"><span class="MathJax_Preview"></span><div class="MathJax_SVG_Display" role="textbox" aria-readonly="true" style="text-align: center;"><span class="MathJax_SVG" id="MathJax-Element-45-Frame" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -771.0516853480245 7004.469099556628 1042.103370696049" style="width: 16.216ex; height: 2.432ex; vertical-align: -0.695ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-68"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-74" x="815" y="-213"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-3D" x="1209" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-46" x="2266" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-28" x="3015" y="0"></use><g transform="translate(3405,0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-78"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-74" x="809" y="-213"></use></g><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-2C" x="4333" y="0"></use><g transform="translate(4778,0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-68"></use><g transform="translate(576,-150)"><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-74"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" 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xlink:href="#MJMATHI-68"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-74" x="815" y="-213"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-3D" x="1209" y="0"></use><g transform="translate(2266,0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-6F"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-74" x="686" y="-213"></use></g><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-2299" x="3329" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-74" x="4330" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-61" x="4691" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-6E" x="5221" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-68" x="5821" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-28" x="6398" y="0"></use><g transform="translate(6787,0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-63"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-74" x="613" y="-213"></use></g><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-29" x="7576" y="0"></use></g></g></svg></span></div><script type="math/tex; mode=display" id="MathJax-Element-147">i_t = \sigma(W_{xi}x_t+W_{hi}h_{h-1}+W_{ci}c_{t-1}+b_i)\\
</p><p data-anchor-id="rwui">循环神经网络按时间展开后如图2所示:在第<span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-25-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -647.0516853480245 361.5 679.103370696049" style="width: 0.811ex; height: 1.622ex; vertical-align: -0.116ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-74"></use></g></svg></span><script type="math/tex" id="MathJax-Element-25">t</script>时刻,网络读入第<span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-26-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -647.0516853480245 361.5 679.103370696049" style="width: 0.811ex; height: 1.622ex; vertical-align: -0.116ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-74"></use></g></svg></span><script type="math/tex" id="MathJax-Element-26">t</script>个输入<span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-27-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -463.0516853480245 928.1191013989369 641.5886520702876" style="width: 2.201ex; height: 1.506ex; vertical-align: -0.463ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-78"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-74" x="809" y="-213"></use></g></svg></span><script type="math/tex" id="MathJax-Element-27">x_t</script>(向量表示)及前一时刻隐层的状态值<span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-28-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -715.0516853480245 1836.5086745365313 893.5886520702876" style="width: 4.286ex; height: 2.085ex; vertical-align: -0.463ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-68"></use><g transform="translate(576,-150)"><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-74"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-2212" x="361" y="0"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-31" x="1140" y="0"></use></g></g></svg></span><script type="math/tex" id="MathJax-Element-28">h_{t-1}</script>(向量表示,<span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-29-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -715.0516853480245 1030.406943983867 901.3668266633396" style="width: 2.432ex; height: 2.085ex; vertical-align: -0.579ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-68"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-30" x="815" y="-213"></use></g></svg></span><script type="math/tex" id="MathJax-Element-29">h_0</script>一般初始化为<span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-30-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -687.0516853480245 500.5 730.103370696049" style="width: 1.158ex; height: 1.737ex; vertical-align: -0.232ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-30"></use></g></svg></span><script type="math/tex" id="MathJax-Element-30">0</script>向量),计算得出本时刻隐层的状态值<span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-31-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -715.0516853480245 932.1191013989369 893.5886520702876" style="width: 2.201ex; height: 2.085ex; vertical-align: -0.463ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-68"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-74" x="815" y="-213"></use></g></svg></span><script type="math/tex" id="MathJax-Element-31">h_t</script>,重复这一步骤直至读完所有输入。如果将循环神经网络所表示的函数记为<span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-32-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -726.0516853480245 550.5 952.103370696049" style="width: 1.274ex; height: 2.201ex; vertical-align: -0.579ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-66"></use></g></svg></span><script type="math/tex" id="MathJax-Element-32">f</script>,则其公式可表示为:</p><div class="md-section-divider"></div><p data-anchor-id="ffs1"><span class="MathJax_Preview"></span><div class="MathJax_SVG_Display" role="textbox" aria-readonly="true" style="text-align: center;"><span class="MathJax_SVG" id="MathJax-Element-33-Frame" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -771.0516853480245 19507.476147537123 1042.103370696049" style="width: 45.29ex; height: 2.432ex; vertical-align: -0.695ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-68"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-74" x="815" y="-213"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-3D" x="1209" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-66" x="2266" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-28" x="2816" y="0"></use><g transform="translate(3206,0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-78"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-74" x="809" y="-213"></use></g><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-2C" x="4134" y="0"></use><g transform="translate(4579,0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-68"></use><g transform="translate(576,-150)"><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-74"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-2212" x="361" y="0"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-31" x="1140" y="0"></use></g></g><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-29" x="6415" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-3D" x="7083" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-3C3" x="8139" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-28" x="8712" y="0"></use><g transform="translate(9101,0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-57"></use><g transform="translate(944,-150)"><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-78"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-68" x="572" y="0"></use></g></g><g transform="translate(10958,0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-78"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-74" x="809" y="-213"></use></g><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-2B" x="12108" y="0"></use><g transform="translate(13109,0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-57"></use><g transform="translate(944,-150)"><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-68"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-68" x="576" y="0"></use></g></g><g transform="translate(14969,0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-68"></use><g transform="translate(576,-150)"><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-68"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-2212" x="576" y="0"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-31" x="1355" y="0"></use></g></g><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-2B" x="17180" y="0"></use><g transform="translate(18180,0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-62"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-68" x="607" y="-213"></use></g><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-29" x="19117" y="0"></use></g></svg></span></div><script type="math/tex; mode=display" id="MathJax-Element-33">h_t=f(x_t,h_{t-1})=\sigma(W_{xh}x_t+W_{hh}h_{h-1}+b_h)</script></p><p data-anchor-id="863e">其中<span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-34-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -704.0516853480245 1856.9656915833432 882.5886520702876" style="width: 4.286ex; height: 2.085ex; vertical-align: -0.463ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-57"></use><g transform="translate(944,-150)"><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-78"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-68" x="572" y="0"></use></g></g></svg></span><script type="math/tex" id="MathJax-Element-34">W_{xh}</script>是输入到隐层的矩阵参数,<span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-35-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -704.0516853480245 1859.7941187080894 882.5886520702876" style="width: 4.286ex; height: 2.085ex; vertical-align: -0.463ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-57"></use><g transform="translate(944,-150)"><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-68"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-68" x="576" y="0"></use></g></g></svg></span><script type="math/tex" id="MathJax-Element-35">W_{hh}</script>是隐层到隐层的矩阵参数,<span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-36-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -715.0516853480245 937.1470593540447 893.5886520702876" style="width: 2.201ex; height: 2.085ex; vertical-align: -0.463ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-62"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-68" x="607" y="-213"></use></g></svg></span><script type="math/tex" id="MathJax-Element-36">b_h</script>为隐层的偏置向量(bias)参数,<span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-37-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -452.0516853480245 572.5 484.10337069604896" style="width: 1.274ex; height: 1.158ex; vertical-align: -0.116ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-3C3"></use></g></svg></span><script type="math/tex" id="MathJax-Element-37">\sigma</script><span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-38-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -715.0516853480245 3528.5 941.103370696049" style="width: 8.224ex; height: 2.201ex; vertical-align: -0.579ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-73"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-69" x="469" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-67" x="815" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-6D" x="1295" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-6F" x="2174" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-69" x="2659" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-64" x="3005" y="0"></use></g></svg></span><script type="math/tex" id="MathJax-Element-38">sigmoid</script>函数。 </p><p data-anchor-id="7ac9">在处理自然语言时,一般会先将词(one-hot表示)映射为其词向量(word embedding)表示,然后再作为循环神经网络每一时刻的输入<span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-39-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -463.0516853480245 928.1191013989369 641.5886520702876" style="width: 2.201ex; height: 1.506ex; vertical-align: -0.463ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-78"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-74" x="809" y="-213"></use></g></svg></span><script type="math/tex" id="MathJax-Element-39">x_t</script>。此外,可以根据实际需要的不同在循环神经网络的隐层上连接其它层。如,可以把一个循环神经网络的隐层输出连接至下一个循环神经网络的输入构建深层(deep or stacked)循环神经网络,或者提取最后一个时刻的隐层状态作为句子表示进而使用分类模型等等。 </p><div class="md-section-divider"></div><h3 data-anchor-id="opm4" id="长短期记忆网络lstm">长短期记忆网络(LSTM)</h3><p data-anchor-id="puym">对于较长的序列数据,循环神经网络的训练过程中容易出现梯度消失或爆炸现象[<a href="#参考文献">6</a>]。为了解决这一问题,Hochreiter S, Schmidhuber J. (1997)提出了LSTM(long short term memory[<a href="#参考文献">5</a>])。 </p><p data-anchor-id="ornj">相比于简单的循环神经网络,LSTM增加了记忆单元<span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-40-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -463.0516853480245 433.5 496.10337069604896" style="width: 1.042ex; height: 1.158ex; vertical-align: -0.116ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-63"></use></g></svg></span><script type="math/tex" id="MathJax-Element-40">c</script>、输入门<span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-41-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -682.0516853480245 345.5 714.103370696049" style="width: 0.811ex; height: 1.622ex; vertical-align: -0.116ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-69"></use></g></svg></span><script type="math/tex" id="MathJax-Element-41">i</script>、遗忘门<span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-42-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -726.0516853480245 550.5 952.103370696049" style="width: 1.274ex; height: 2.201ex; vertical-align: -0.579ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-66"></use></g></svg></span><script type="math/tex" id="MathJax-Element-42">f</script>及输出门<span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-43-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -462.0516853480245 485.5 494.10337069604896" style="width: 1.158ex; height: 1.158ex; vertical-align: -0.116ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-6F"></use></g></svg></span><script type="math/tex" id="MathJax-Element-43">o</script>。这些门及记忆单元组合起来大大提升了循环神经网络处理长序列数据的能力。若将基于LSTM的循环神经网络表示的函数记为<span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-44-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -701.0516853480245 749.5 722.103370696049" style="width: 1.737ex; height: 1.622ex; vertical-align: -0.116ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-46"></use></g></svg></span><script type="math/tex" id="MathJax-Element-44">F</script>,则其公式为:</p><div class="md-section-divider"></div><p data-anchor-id="5cdo"><span class="MathJax_Preview"></span><div class="MathJax_SVG_Display" role="textbox" aria-readonly="true" style="text-align: center;"><span class="MathJax_SVG" id="MathJax-Element-45-Frame" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -771.0516853480245 7004.469099556628 1042.103370696049" style="width: 16.216ex; height: 2.432ex; vertical-align: -0.695ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-68"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-74" x="815" y="-213"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-3D" x="1209" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-46" x="2266" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-28" x="3015" y="0"></use><g transform="translate(3405,0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-78"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-74" x="809" y="-213"></use></g><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-2C" x="4333" y="0"></use><g transform="translate(4778,0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-68"></use><g transform="translate(576,-150)"><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-74"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-2212" x="361" y="0"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-31" x="1140" y="0"></use></g></g><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-29" x="6614" y="0"></use></g></svg></span></div><script type="math/tex; mode=display" id="MathJax-Element-45"> h_t=F(x_t,h_{t-1})</script></p><p data-anchor-id="51da"><span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-46-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -701.0516853480245 749.5 722.103370696049" style="width: 1.737ex; height: 1.622ex; vertical-align: -0.116ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-46"></use></g></svg></span><script type="math/tex" id="MathJax-Element-46">F</script>由下列公式组合而成[<a href="#参考文献">7</a>]:</p><div class="md-section-divider"></div><p data-anchor-id="x9vt"><span class="MathJax_Preview"></span><div class="MathJax_SVG_Display" role="textbox" aria-readonly="true"><span class="MathJax_SVG" id="MathJax-Element-47-Frame" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -771.0516853480245 39896.895752895754 6821.757555138181" style="width: 92.664ex; height: 15.869ex; vertical-align: -14.131ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><g transform="translate(11236,0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-69"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-74" x="488" y="-213"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-3D" x="978" y="0"></use><use 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y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-6E" x="9923" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-68" x="10524" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-28" x="11100" y="0"></use><g transform="translate(11490,0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-57"></use><g transform="translate(944,-150)"><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-78"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-63" x="572" y="0"></use></g></g><g transform="translate(13246,0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-78"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-74" x="809" y="-213"></use></g><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-2B" x="14396" y="0"></use><g transform="translate(15397,0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-57"></use><g transform="translate(944,-150)"><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-68"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-63" x="576" y="0"></use></g></g><g transform="translate(17155,0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-68"></use><g transform="translate(576,-150)"><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-68"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-2212" x="576" y="0"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-31" x="1355" y="0"></use></g></g><use 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transform="translate(3137,0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-57"></use><g transform="translate(944,-150)"><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-78"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-6F" x="572" y="0"></use></g></g><g transform="translate(4929,0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-78"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-74" x="809" y="-213"></use></g><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-2B" x="6080" y="0"></use><g transform="translate(7080,0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-57"></use><g transform="translate(944,-150)"><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-68"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-6F" x="576" y="0"></use></g></g><g transform="translate(8876,0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-68"></use><g transform="translate(576,-150)"><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-68"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-2212" x="576" y="0"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-31" x="1355" y="0"></use></g></g><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-2B" x="11087" y="0"></use><g transform="translate(12087,0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-57"></use><g transform="translate(944,-150)"><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-63"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-6F" x="433" y="0"></use></g></g><g transform="translate(13782,0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-63"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-74" x="613" y="-213"></use></g><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-2B" x="14793" y="0"></use><g transform="translate(15794,0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-62"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-6F" x="607" y="-213"></use></g><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-29" x="16666" y="0"></use></g><g transform="translate(15965,-5780)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-68"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-74" x="815" y="-213"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-3D" x="1209" y="0"></use><g transform="translate(2266,0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-6F"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-74" x="686" y="-213"></use></g><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-2299" x="3329" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-74" x="4330" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-61" x="4691" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-6E" x="5221" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-68" x="5821" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-28" x="6398" y="0"></use><g transform="translate(6787,0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-63"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-74" x="613" y="-213"></use></g><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-29" x="7576" y="0"></use></g></g></svg></span></div><script type="math/tex; mode=display" id="MathJax-Element-47">i_t = \sigma(W_{xi}x_t+W_{hi}h_{h-1}+W_{ci}c_{t-1}+b_i)\\
f_t = \sigma(W_{xf}x_t+W_{hf}h_{h-1}+W_{cf}c_{t-1}+b_f)\\
c_t = f_t\odot c_{t-1}+i_t\odot tanh(W_{xc}x_t+W_{hc}h_{h-1}+b_c)\\
o_t = \sigma(W_{xo}x_t+W_{ho}h_{h-1}+W_{co}c_{t}+b_o)\\
h_t = o_t\odot tanh(c_t)</script> <br>
其中,<span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-148-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -726.0516853480245 4512.976405595748 952.103370696049" style="width: 10.425ex; height: 2.201ex; vertical-align: -0.579ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-69"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-74" x="488" y="-213"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-2C" x="701" y="0"></use><g transform="translate(1146,0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-66"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-74" x="693" y="-213"></use></g><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-2C" x="1992" y="0"></use><g transform="translate(2437,0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-63"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-74" x="613" y="-213"></use></g><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-2C" x="3226" y="0"></use><g transform="translate(3671,0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-6F"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-74" x="686" y="-213"></use></g></g></svg></span><script type="math/tex" id="MathJax-Element-148">i_t, f_t, c_t, o_t</script>分别表示输入门,遗忘门,记忆单元及输出门的向量值,带角标的<span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-149-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -704.0516853480245 1048.5 747.103370696049" style="width: 2.432ex; height: 1.737ex; vertical-align: -0.232ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-57"></use></g></svg></span><script type="math/tex" id="MathJax-Element-149">W</script><span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-150-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -715.0516853480245 429.5 747.103370696049" style="width: 1.042ex; height: 1.737ex; vertical-align: -0.116ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-62"></use></g></svg></span><script type="math/tex" id="MathJax-Element-150">b</script>为模型参数,<span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-151-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -715.0516853480245 2068 747.103370696049" style="width: 4.749ex; height: 1.737ex; vertical-align: -0.116ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-74"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-61" x="361" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-6E" x="891" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-68" x="1491" y="0"></use></g></svg></span><script type="math/tex" id="MathJax-Element-151">tanh</script>为双曲正切函数,<span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-152-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -604.0516853480245 778.5 708.103370696049" style="width: 1.853ex; height: 1.622ex; vertical-align: -0.347ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-2299"></use></g></svg></span><script type="math/tex" id="MathJax-Element-152">\odot</script>表示逐元素(elementwise)的乘法操作。输入门控制着新输入进入记忆单元<span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-153-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -463.0516853480245 433.5 496.10337069604896" style="width: 1.042ex; height: 1.158ex; vertical-align: -0.116ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-63"></use></g></svg></span><script type="math/tex" id="MathJax-Element-153">c</script>的强度,遗忘门控制着记忆单元维持上一时刻值的强度,输出门控制着输出记忆单元的强度。三种门的计算方式类似,但有着完全不同的参数,它们各自以不同的方式控制着记忆单元<span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-154-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -463.0516853480245 433.5 496.10337069604896" style="width: 1.042ex; height: 1.158ex; vertical-align: -0.116ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-63"></use></g></svg></span><script type="math/tex" id="MathJax-Element-154">c</script>,如图3所示:</p><p align="center" data-anchor-id="gztx">
其中,<span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-48-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -726.0516853480245 4512.976405595748 952.103370696049" style="width: 10.425ex; height: 2.201ex; vertical-align: -0.579ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-69"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-74" x="488" y="-213"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-2C" x="701" y="0"></use><g transform="translate(1146,0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-66"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-74" x="693" y="-213"></use></g><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-2C" x="1992" y="0"></use><g transform="translate(2437,0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-63"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-74" x="613" y="-213"></use></g><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-2C" x="3226" y="0"></use><g transform="translate(3671,0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-6F"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-74" x="686" y="-213"></use></g></g></svg></span><script type="math/tex" id="MathJax-Element-48">i_t, f_t, c_t, o_t</script>分别表示输入门,遗忘门,记忆单元及输出门的向量值,带角标的<span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-49-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -704.0516853480245 1048.5 747.103370696049" style="width: 2.432ex; height: 1.737ex; vertical-align: -0.232ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-57"></use></g></svg></span><script type="math/tex" id="MathJax-Element-49">W</script><span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-50-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -715.0516853480245 429.5 747.103370696049" style="width: 1.042ex; height: 1.737ex; vertical-align: -0.116ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-62"></use></g></svg></span><script type="math/tex" id="MathJax-Element-50">b</script>为模型参数,<span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-51-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -715.0516853480245 2068 747.103370696049" style="width: 4.749ex; height: 1.737ex; vertical-align: -0.116ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-74"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-61" x="361" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-6E" x="891" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-68" x="1491" y="0"></use></g></svg></span><script type="math/tex" id="MathJax-Element-51">tanh</script>为双曲正切函数,<span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-52-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -604.0516853480245 778.5 708.103370696049" style="width: 1.853ex; height: 1.622ex; vertical-align: -0.347ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-2299"></use></g></svg></span><script type="math/tex" id="MathJax-Element-52">\odot</script>表示逐元素(elementwise)的乘法操作。输入门控制着新输入进入记忆单元<span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-53-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -463.0516853480245 433.5 496.10337069604896" style="width: 1.042ex; height: 1.158ex; vertical-align: -0.116ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-63"></use></g></svg></span><script type="math/tex" id="MathJax-Element-53">c</script>的强度,遗忘门控制着记忆单元维持上一时刻值的强度,输出门控制着输出记忆单元的强度。三种门的计算方式类似,但有着完全不同的参数,它们各自以不同的方式控制着记忆单元<span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-54-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -463.0516853480245 433.5 496.10337069604896" style="width: 1.042ex; height: 1.158ex; vertical-align: -0.116ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-63"></use></g></svg></span><script type="math/tex" id="MathJax-Element-54">c</script>,如图3所示:</p><p align="center" data-anchor-id="gztx">
<img src="https://raw.githubusercontent.com/PaddlePaddle/book/develop/understand_sentiment/image/lstm.png" width="600"><br>
图3. 时刻<span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-60-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -647.0516853480245 361.5 679.103370696049" style="width: 0.811ex; height: 1.622ex; vertical-align: -0.116ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-74"></use></g></svg></span><script type="math/tex" id="MathJax-Element-60">t</script>的LSTM [7]
图3. 时刻<span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-55-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -647.0516853480245 361.5 679.103370696049" style="width: 0.811ex; height: 1.622ex; vertical-align: -0.116ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-74"></use></g></svg></span><script type="math/tex" id="MathJax-Element-55">t</script>的LSTM [7]
</p><p data-anchor-id="jbb7">LSTM通过给简单的循环神经网络增加记忆及控制门的方式,增强了其处理远距离依赖问题的能力。类似原理的改进还有Gated Recurrent Unit (GRU)[<a href="#参考文献">8</a>],其设计更为简洁一些。<strong>这些改进虽然各有不同,但是它们的宏观描述却与简单的循环神经网络一样(如图2所示),即隐状态依据当前输入及前一时刻的隐状态来改变,不断地循环这一过程直至输入处理完毕:</strong></p><div class="md-section-divider"></div><p data-anchor-id="p2ku"><span class="MathJax_Preview"></span><div class="MathJax_SVG_Display" role="textbox" aria-readonly="true" style="text-align: center;"><span class="MathJax_SVG" id="MathJax-Element-56-Frame" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -771.0516853480245 10818.469099556627 1042.103370696049" style="width: 25.135ex; height: 2.432ex; vertical-align: -0.695ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-68"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-74" x="815" y="-213"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-3D" x="1209" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-52" x="2266" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-65" x="3025" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-63" x="3492" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-72" x="3925" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-75" x="4377" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-72" x="4949" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-65" x="5401" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-6E" x="5867" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-74" x="6468" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-28" x="6829" y="0"></use><g transform="translate(7219,0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-78"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-74" x="809" y="-213"></use></g><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-2C" x="8147" y="0"></use><g transform="translate(8592,0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-68"></use><g transform="translate(576,-150)"><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-74"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-2212" x="361" y="0"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-31" x="1140" y="0"></use></g></g><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMAIN-29" x="10428" y="0"></use></g></svg></span></div><script type="math/tex; mode=display" id="MathJax-Element-56"> h_t=Recrurent(x_t,h_{t-1})</script></p><p data-anchor-id="dmbf">其中,<span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-57-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -704.0516853480245 4563.5 746.103370696049" style="width: 10.656ex; height: 1.737ex; vertical-align: -0.232ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-52"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-65" x="759" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-63" x="1226" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-72" x="1659" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-75" x="2111" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-72" x="2683" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-65" x="3135" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-6E" x="3601" y="0"></use><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-74" x="4202" y="0"></use></g></svg></span><script type="math/tex" id="MathJax-Element-57">Recrurent</script>可以表示简单的循环神经网络、GRU或LSTM。</p><div class="md-section-divider"></div><h3 data-anchor-id="ub28" id="栈式双向lstmstacked-bidirectional-lstm">栈式双向LSTM(Stacked Bidirectional LSTM)</h3><p data-anchor-id="af1z">对于正常顺序的循环神经网络,<span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-58-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -715.0516853480245 932.1191013989369 893.5886520702876" style="width: 2.201ex; height: 2.085ex; vertical-align: -0.463ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-68"></use><use transform="scale(0.7071067811865476)" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-74" x="815" y="-213"></use></g></svg></span><script type="math/tex" id="MathJax-Element-58">h_t</script>包含了<span class="MathJax_Preview"></span><span class="MathJax_SVG" id="MathJax-Element-59-Frame" role="textbox" aria-readonly="true" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 -647.0516853480245 361.5 679.103370696049" style="width: 0.811ex; height: 1.622ex; vertical-align: -0.116ex; margin: 1px 0px;"><g stroke="black" fill="black" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#MJMATHI-74"></use></g></svg></span><script type="math/tex" id="MathJax-Element-59">t</script>时刻之前的输入信息,也就是上文信息。同样,为了得到下文信息,我们可以使用反方向(将输入逆序处理)的循环神经网络。结合构建深层循环神经网络的方法(深层神经网络往往能得到更抽象和高级的特征表示),我们可以通过构建更加强有力的基于LSTM的栈式双向循环神经网络[<a href="#参考文献">9</a>],来对时序数据进行建模。 </p><p data-anchor-id="ozsi">如图4所示(以三层为例),奇数层LSTM正向,偶数层LSTM反向,高一层的LSTM使用低一层LSTM及之前所有层的信息作为输入,对最高层LSTM序列使用时间维度上的最大池化即可得到文本的定长向量表示(这一表示充分融合了文本的上下文信息,并且对文本进行了深层次抽象),最后我们将文本表示连接至softmax构建分类模型。</p><p align="center" data-anchor-id="9fkt">
<img src="https://raw.githubusercontent.com/PaddlePaddle/book/develop/understand_sentiment/image/stacked_lstm.jpg" width="450"><br>
图4. 栈式双向LSTM用于文本分类
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