Skip to content

P
Paddle

PaddlePaddle / Paddle
大约 1 年 前同步成功

通知 2298
Star 20931
Fork 5422
P
Paddle
切换分支/标签
查找文件 普通视图历史永久链接Permalink
error_clip.html 26.8 KB
Newer Older
T
Deploy to GitHub Pages: 6ece41ecb92bab7c7615c8d46906dc1df2237a80  
Travis CI 已提交
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 


<!DOCTYPE html>
<!--[if IE 8]><html class="no-js lt-ie9" lang="en" > <![endif]-->
<!--[if gt IE 8]><!--> <html class="no-js" lang="en" > <!--<![endif]-->
<head>
  <meta charset="utf-8">
  
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  
  <title>Error Clip &mdash; PaddlePaddle  文档</title>
  

  
  

  

  
  
    

  

  
  
    <link rel="stylesheet" href="../_static/css/theme.css" type="text/css" />
  

  
  
        <link rel="index" title="索引"
              href="../genindex.html"/>
        <link rel="search" title="搜索" href="../search.html"/>
    <link rel="top" title="PaddlePaddle  文档" href="../index.html"/> 

  <link rel="stylesheet" href="https://cdn.jsdelivr.net/perfect-scrollbar/0.6.14/css/perfect-scrollbar.min.css" type="text/css" />
  <link rel="stylesheet" href="../_static/css/override.css" type="text/css" />
  <script>
  var _hmt = _hmt || [];
  (function() {
    var hm = document.createElement("script");
    hm.src = "//hm.baidu.com/hm.js?b9a314ab40d04d805655aab1deee08ba";
    var s = document.getElementsByTagName("script")[0]; 
    s.parentNode.insertBefore(hm, s);
  })();
  </script>

  

  
  <script src="../_static/js/modernizr.min.js"></script>

</head>

<body class="wy-body-for-nav" role="document">

  
  <header class="site-header">
    <div class="site-logo">
      <a href="/"><img src="../_static/images/PP_w.png"></a>
    </div>
    <div class="site-nav-links">
      <div class="site-menu">
        <a class="fork-on-github" href="https://github.com/PaddlePaddle/Paddle" target="_blank"><i class="fa fa-github"></i>Fork me on Github</a>
        <div class="language-switcher dropdown">
          <a type="button" data-toggle="dropdown">
            <span>English</span>
            <i class="fa fa-angle-up"></i>
            <i class="fa fa-angle-down"></i>
          </a>
          <ul class="dropdown-menu">
            <li><a href="/doc_cn">中文</a></li>
            <li><a href="/doc">English</a></li>
          </ul>
        </div>
        <ul class="site-page-links">
          <li><a href="/">Home</a></li>
        </ul>
      </div>
      <div class="doc-module">
        
        <ul>
<li class="toctree-l1"><a class="reference internal" href="../getstarted/index_cn.html">新手入门</a></li>
<li class="toctree-l1"><a class="reference internal" href="../howto/index_cn.html">进阶指南</a></li>
<li class="toctree-l1"><a class="reference internal" href="../api/index_cn.html">API</a></li>
<li class="toctree-l1"><a class="reference internal" href="../faq/index_cn.html">FAQ</a></li>
<li class="toctree-l1"><a class="reference internal" href="../mobile/index_cn.html">MOBILE</a></li>
</ul>

        
<div role="search">
  <form id="rtd-search-form" class="wy-form" action="../search.html" method="get">
    <input type="text" name="q" placeholder="Search docs" />
    <input type="hidden" name="check_keywords" value="yes" />
    <input type="hidden" name="area" value="default" />
  </form>
</div>        
      </div>
    </div>
  </header>
  
  <div class="main-content-wrap">

    
    <nav class="doc-menu-vertical" role="navigation">
        
          
          <ul>
<li class="toctree-l1"><a class="reference internal" href="../getstarted/index_cn.html">新手入门</a><ul>
<li class="toctree-l2"><a class="reference internal" href="../getstarted/build_and_install/index_cn.html">安装与编译</a><ul>
<li class="toctree-l3"><a class="reference internal" href="../getstarted/build_and_install/pip_install_cn.html">使用pip安装</a></li>
<li class="toctree-l3"><a class="reference internal" href="../getstarted/build_and_install/docker_install_cn.html">使用Docker安装运行</a></li>
<li class="toctree-l3"><a class="reference internal" href="../howto/dev/build_cn.html">用Docker编译和测试PaddlePaddle</a></li>
<li class="toctree-l3"><a class="reference internal" href="../getstarted/build_and_install/build_from_source_cn.html">从源码编译</a></li>
</ul>
</li>
<li class="toctree-l2"><a class="reference internal" href="../getstarted/concepts/use_concepts_cn.html">基本使用概念</a></li>
</ul>
</li>
<li class="toctree-l1"><a class="reference internal" href="../howto/index_cn.html">进阶指南</a><ul>
<li class="toctree-l2"><a class="reference internal" href="../howto/usage/cmd_parameter/index_cn.html">设置命令行参数</a><ul>
<li class="toctree-l3"><a class="reference internal" href="../howto/usage/cmd_parameter/use_case_cn.html">使用案例</a></li>
<li class="toctree-l3"><a class="reference internal" href="../howto/usage/cmd_parameter/arguments_cn.html">参数概述</a></li>
<li class="toctree-l3"><a class="reference internal" href="../howto/usage/cmd_parameter/detail_introduction_cn.html">细节描述</a></li>
</ul>
</li>
<li class="toctree-l2"><a class="reference internal" href="../howto/usage/cluster/cluster_train_cn.html">分布式训练</a><ul>
<li class="toctree-l3"><a class="reference internal" href="../howto/usage/cluster/fabric_cn.html">fabric集群</a></li>
<li class="toctree-l3"><a class="reference internal" href="../howto/usage/cluster/openmpi_cn.html">openmpi集群</a></li>
<li class="toctree-l3"><a class="reference internal" href="../howto/usage/cluster/k8s_cn.html">kubernetes单机</a></li>
<li class="toctree-l3"><a class="reference internal" href="../howto/usage/cluster/k8s_distributed_cn.html">kubernetes distributed分布式</a></li>
<li class="toctree-l3"><a class="reference internal" href="../howto/usage/cluster/k8s_aws_cn.html">AWS上运行kubernetes集群训练</a></li>
</ul>
</li>
<li class="toctree-l2"><a class="reference internal" href="../howto/dev/contribute_to_paddle_cn.html">如何贡献代码</a></li>
<li class="toctree-l2"><a class="reference internal" href="../howto/dev/write_docs_cn.html">如何贡献/修改文档</a></li>
<li class="toctree-l2"><a class="reference internal" href="../howto/deep_model/rnn/index_cn.html">RNN相关模型</a><ul>
<li class="toctree-l3"><a class="reference internal" href="../howto/deep_model/rnn/rnn_config_cn.html">RNN配置</a></li>
<li class="toctree-l3"><a class="reference internal" href="../howto/deep_model/rnn/recurrent_group_cn.html">Recurrent Group教程</a></li>
<li class="toctree-l3"><a class="reference internal" href="../howto/deep_model/rnn/hierarchical_layer_cn.html">支持双层序列作为输入的Layer</a></li>
<li class="toctree-l3"><a class="reference internal" href="../howto/deep_model/rnn/hrnn_rnn_api_compare_cn.html">单双层RNN API对比介绍</a></li>
</ul>
</li>
<li class="toctree-l2"><a class="reference internal" href="../howto/optimization/gpu_profiling_cn.html">GPU性能分析与调优</a></li>
</ul>
</li>
<li class="toctree-l1"><a class="reference internal" href="../api/index_cn.html">API</a><ul>
<li class="toctree-l2"><a class="reference internal" href="../api/v2/model_configs.html">模型配置</a><ul>
<li class="toctree-l3"><a class="reference internal" href="../api/v2/config/activation.html">Activation</a></li>
<li class="toctree-l3"><a class="reference internal" href="../api/v2/config/layer.html">Layers</a></li>
<li class="toctree-l3"><a class="reference internal" href="../api/v2/config/evaluators.html">Evaluators</a></li>
<li class="toctree-l3"><a class="reference internal" href="../api/v2/config/optimizer.html">Optimizer</a></li>
<li class="toctree-l3"><a class="reference internal" href="../api/v2/config/pooling.html">Pooling</a></li>
<li class="toctree-l3"><a class="reference internal" href="../api/v2/config/networks.html">Networks</a></li>
<li class="toctree-l3"><a class="reference internal" href="../api/v2/config/attr.html">Parameter Attribute</a></li>
</ul>
</li>
<li class="toctree-l2"><a class="reference internal" href="../api/v2/data.html">数据访问</a><ul>
<li class="toctree-l3"><a class="reference internal" href="../api/v2/data/data_reader.html">Data Reader Interface</a></li>
<li class="toctree-l3"><a class="reference internal" href="../api/v2/data/image.html">Image Interface</a></li>
<li class="toctree-l3"><a class="reference internal" href="../api/v2/data/dataset.html">Dataset</a></li>
</ul>
</li>
<li class="toctree-l2"><a class="reference internal" href="../api/v2/run_logic.html">训练与应用</a></li>
<li class="toctree-l2"><a class="reference internal" href="../api/v2/fluid.html">Fluid</a><ul>
<li class="toctree-l3"><a class="reference internal" href="../api/v2/fluid/layers.html">Layers</a></li>
<li class="toctree-l3"><a class="reference internal" href="../api/v2/fluid/data_feeder.html">DataFeeder</a></li>
<li class="toctree-l3"><a class="reference internal" href="../api/v2/fluid/executor.html">Executor</a></li>
<li class="toctree-l3"><a class="reference internal" href="../api/v2/fluid/initializer.html">Initializer</a></li>
<li class="toctree-l3"><a class="reference internal" href="../api/v2/fluid/evaluator.html">Evaluator</a></li>
<li class="toctree-l3"><a class="reference internal" href="../api/v2/fluid/nets.html">Nets</a></li>
<li class="toctree-l3"><a class="reference internal" href="../api/v2/fluid/optimizer.html">Optimizer</a></li>
<li class="toctree-l3"><a class="reference internal" href="../api/v2/fluid/param_attr.html">ParamAttr</a></li>
<li class="toctree-l3"><a class="reference internal" href="../api/v2/fluid/profiler.html">Profiler</a></li>
<li class="toctree-l3"><a class="reference internal" href="../api/v2/fluid/regularizer.html">Regularizer</a></li>
</ul>
</li>
</ul>
</li>
<li class="toctree-l1"><a class="reference internal" href="../faq/index_cn.html">FAQ</a><ul>
<li class="toctree-l2"><a class="reference internal" href="../faq/build_and_install/index_cn.html">编译安装与单元测试</a></li>
<li class="toctree-l2"><a class="reference internal" href="../faq/model/index_cn.html">模型配置</a></li>
<li class="toctree-l2"><a class="reference internal" href="../faq/parameter/index_cn.html">参数设置</a></li>
<li class="toctree-l2"><a class="reference internal" href="../faq/local/index_cn.html">本地训练与预测</a></li>
<li class="toctree-l2"><a class="reference internal" href="../faq/cluster/index_cn.html">集群训练与预测</a></li>
</ul>
</li>
<li class="toctree-l1"><a class="reference internal" href="../mobile/index_cn.html">MOBILE</a><ul>
<li class="toctree-l2"><a class="reference internal" href="../mobile/cross_compiling_for_android_cn.html">Android平台编译指南</a></li>
<li class="toctree-l2"><a class="reference internal" href="../mobile/cross_compiling_for_ios_cn.html">iOS平台编译指南</a></li>
<li class="toctree-l2"><a class="reference internal" href="../mobile/cross_compiling_for_raspberry_cn.html">Raspberry Pi平台编译指南</a></li>
</ul>
</li>
</ul>

        
    </nav>
    
    <section class="doc-content-wrap">

      

 







<div role="navigation" aria-label="breadcrumbs navigation">
  <ul class="wy-breadcrumbs">
      
    <li>Error Clip</li>
  </ul>
</div>
      
      <div class="wy-nav-content" id="doc-content">
        <div class="rst-content">
          <div role="main" class="document" itemscope="itemscope" itemtype="http://schema.org/Article">
           <div itemprop="articleBody">
            
  <div class="section" id="error-clip">
<span id="error-clip"></span><h1>Error Clip<a class="headerlink" href="#error-clip" title="永久链接至标题"></a></h1>
<div class="section" id="overview">
<span id="overview"></span><h2>Overview<a class="headerlink" href="#overview" title="永久链接至标题"></a></h2>
<p>Error clip is widely used in model training to prevent gradient exploding. It takes some specific rules to adjust variables&#8217; gradients and prevent them from being too large. With it, values of a gradient will be checked before they are taken by the next <code class="docutils literal"><span class="pre">grad_op</span></code> and be shrunk if necessary.</p>
</div>
<div class="section" id="usage">
<span id="usage"></span><h2>Usage<a class="headerlink" href="#usage" title="永久链接至标题"></a></h2>
<p>Users are allowed to assign different error clip methods or attributes to different <code class="docutils literal"><span class="pre">Variable</span></code>s. Users can specify it as a parameter of <code class="docutils literal"><span class="pre">Variable</span></code>&#8216;s constructor:</p>
<div class="highlight-python"><div class="highlight"><pre><span></span><span class="n">var</span> <span class="o">=</span> <span class="n">framework</span><span class="o">.</span><span class="n">Variable</span><span class="p">(</span><span class="o">...</span><span class="p">,</span> <span class="n">error_clip</span><span class="o">=</span><span class="n">myErrorClip</span><span class="p">,</span> <span class="o">...</span><span class="p">)</span>
</pre></div>
</div>
<p>The default value of <code class="docutils literal"><span class="pre">error_clip</span></code> is <code class="docutils literal"><span class="pre">None</span></code>, which means no error clip is employed. When it&#8217;s not <code class="docutils literal"><span class="pre">None</span></code>, it should take an object of <code class="docutils literal"><span class="pre">BaseErrorClipAttr</span></code>&#8216;s derived class. So far, <code class="docutils literal"><span class="pre">BaseErrorClipAttr</span></code> has only one derived class: <code class="docutils literal"><span class="pre">ErrorClipByValue</span></code>, whose constructor is:</p>
<div class="highlight-python"><div class="highlight"><pre><span></span><span class="n">ErrorClipByValue</span><span class="p">(</span><span class="nb">max</span><span class="p">,</span> <span class="nb">min</span><span class="o">=</span><span class="bp">None</span><span class="p">)</span>
</pre></div>
</div>
<p><code class="docutils literal"><span class="pre">max</span></code> and <code class="docutils literal"><span class="pre">min</span></code> represent the maximal and minimal clip threshold respectively. In backward pass, all values of <code class="docutils literal"><span class="pre">var</span></code>&#8216;s gradient greater than <code class="docutils literal"><span class="pre">max</span></code> or less than <code class="docutils literal"><span class="pre">min</span></code> will be clipped to <code class="docutils literal"><span class="pre">max</span></code> and <code class="docutils literal"><span class="pre">min</span></code> respectively. When the <code class="docutils literal"><span class="pre">min</span></code> is None, the minimal threshold will be assigned with <code class="docutils literal"><span class="pre">-max</span></code> automatically.</p>
<p>So we can enable the error clip with threshold <code class="docutils literal"><span class="pre">[-5.0,</span> <span class="pre">5.0]</span></code> for variable <code class="docutils literal"><span class="pre">var</span></code> by:</p>
<div class="highlight-python"><div class="highlight"><pre><span></span><span class="n">var</span> <span class="o">=</span> <span class="n">framework</span><span class="o">.</span><span class="n">Variable</span><span class="p">(</span><span class="o">...</span><span class="p">,</span> <span class="n">error_clip</span><span class="o">=</span><span class="n">ErrorClipByValue</span><span class="p">(</span><span class="nb">max</span><span class="o">=</span><span class="mf">5.0</span><span class="p">),</span> <span class="o">...</span><span class="p">)</span>
</pre></div>
</div>
</div>
<div class="section" id="implementation">
<span id="implementation"></span><h2>Implementation<a class="headerlink" href="#implementation" title="永久链接至标题"></a></h2>
<p>The <code class="docutils literal"><span class="pre">BaseErrorClipAttr</span></code> and its derived class <code class="docutils literal"><span class="pre">ErrorClipByValue</span></code> are defined in <em>clip.py</em>.</p>
<div class="highlight-python"><div class="highlight"><pre><span></span><span class="k">class</span> <span class="nc">BaseErrorClipAttr</span><span class="p">(</span><span class="nb">object</span><span class="p">):</span>
    <span class="k">def</span> <span class="nf">append_clip_op</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">block</span><span class="p">,</span> <span class="n">grad_name</span><span class="p">):</span>
        <span class="k">raise</span> <span class="ne">NotImplementedError</span><span class="p">()</span>


<span class="k">class</span> <span class="nc">ErrorClipByValue</span><span class="p">(</span><span class="n">BaseErrorClipAttr</span><span class="p">):</span>
    <span class="k">def</span> <span class="fm">__init__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="nb">max</span><span class="p">,</span> <span class="nb">min</span><span class="o">=</span><span class="bp">None</span><span class="p">):</span>
        <span class="nb">max</span> <span class="o">=</span> <span class="nb">float</span><span class="p">(</span><span class="nb">max</span><span class="p">)</span>
        <span class="k">if</span> <span class="nb">min</span> <span class="ow">is</span> <span class="bp">None</span><span class="p">:</span>
            <span class="nb">min</span> <span class="o">=</span> <span class="o">-</span><span class="nb">max</span>
        <span class="k">else</span><span class="p">:</span>
            <span class="nb">min</span> <span class="o">=</span> <span class="nb">float</span><span class="p">(</span><span class="nb">min</span><span class="p">)</span>
        <span class="bp">self</span><span class="o">.</span><span class="n">max</span> <span class="o">=</span> <span class="nb">max</span>
        <span class="bp">self</span><span class="o">.</span><span class="n">min</span> <span class="o">=</span> <span class="nb">min</span>

    <span class="k">def</span> <span class="nf">append_clip_op</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">block</span><span class="p">,</span> <span class="n">grad_name</span><span class="p">):</span>
        <span class="n">block</span><span class="o">.</span><span class="n">append_op</span><span class="p">(</span>
            <span class="nb">type</span><span class="o">=</span><span class="s2">&quot;clip&quot;</span><span class="p">,</span>
            <span class="n">inputs</span><span class="o">=</span><span class="p">{</span><span class="s2">&quot;X&quot;</span><span class="p">:</span> <span class="n">grad_name</span><span class="p">},</span>
            <span class="n">outputs</span><span class="o">=</span><span class="p">{</span><span class="s2">&quot;Out&quot;</span><span class="p">:</span> <span class="n">grad_name</span><span class="p">},</span>
            <span class="n">attrs</span><span class="o">=</span><span class="p">{</span><span class="s2">&quot;min&quot;</span><span class="p">:</span> <span class="bp">self</span><span class="o">.</span><span class="n">min</span><span class="p">,</span>
                   <span class="s2">&quot;max&quot;</span><span class="p">:</span> <span class="bp">self</span><span class="o">.</span><span class="n">max</span><span class="p">})</span>
</pre></div>
</div>
<p>The <code class="docutils literal"><span class="pre">BaseErrorClipAttr</span></code> have one main member functions: <code class="docutils literal"><span class="pre">append_clip_op(self,</span> <span class="pre">block,</span> <span class="pre">grad_name)</span></code>.</p>
<p>This function is used to create a <code class="docutils literal"><span class="pre">clip_op</span></code> and append it to the end of given <code class="docutils literal"><span class="pre">block</span></code>. For different error clip algorithm require different <code class="docutils literal"><span class="pre">clip_op</span></code>, the function is defined as virtual in the base class. All derived classes must implement their own versions of this function.</p>
<p>These <code class="docutils literal"><span class="pre">clip_op</span></code>s should be inserted after <code class="docutils literal"><span class="pre">grad_op</span></code>s whose output gradients need to be clipped. It is equivalent to appending some <code class="docutils literal"><span class="pre">clip_op</span></code>s to the end of the target block every time a new <code class="docutils literal"><span class="pre">grad_op</span></code> is added.</p>
<div class="highlight-python"><div class="highlight"><pre><span></span><span class="k">for</span> <span class="n">op_desc</span> <span class="ow">in</span> <span class="n">grad_op_descs</span><span class="p">:</span>
        <span class="n">new_op_desc</span> <span class="o">=</span> <span class="n">target_block</span><span class="o">.</span><span class="n">desc</span><span class="o">.</span><span class="n">append_op</span><span class="p">()</span>
        <span class="n">new_op_desc</span><span class="o">.</span><span class="n">copy_from</span><span class="p">(</span><span class="n">op_desc</span><span class="p">)</span>
        <span class="n">callback</span><span class="p">(</span><span class="n">block</span><span class="o">=</span><span class="n">target_block</span><span class="p">,</span> <span class="n">context</span><span class="o">=</span><span class="n">grad_to_var</span><span class="p">)</span>
</pre></div>
</div>
<p>Here we employ a callback function to complete this kind of jobs. In <code class="docutils literal"><span class="pre">_append_backward_ops_</span></code> function, each time after a <code class="docutils literal"><span class="pre">grad_op</span></code> is added to the <code class="docutils literal"><span class="pre">target_block</span></code>, a callback function is invoked. The logic of <code class="docutils literal"><span class="pre">clip_op</span></code> appending can be implemented inside the callback function.</p>
<p>The callback function for <code class="docutils literal"><span class="pre">clip_op</span></code> appending is defined in <em>clip.py</em>:</p>
<div class="highlight-python"><div class="highlight"><pre><span></span><span class="k">def</span> <span class="nf">error_clip_callback</span><span class="p">(</span><span class="n">block</span><span class="p">,</span> <span class="n">context</span><span class="p">):</span>
    <span class="c1"># the context is a grad_to_var map</span>
    <span class="n">grad_to_var</span> <span class="o">=</span> <span class="n">context</span>
    <span class="n">op_desc</span> <span class="o">=</span> <span class="n">block</span><span class="o">.</span><span class="n">desc</span><span class="o">.</span><span class="n">op</span><span class="p">(</span><span class="n">block</span><span class="o">.</span><span class="n">desc</span><span class="o">.</span><span class="n">op_size</span><span class="p">()</span> <span class="o">-</span> <span class="mi">1</span><span class="p">)</span>
    <span class="k">for</span> <span class="n">grad_n</span> <span class="ow">in</span> <span class="nb">filter</span><span class="p">(</span><span class="k">lambda</span> <span class="n">n</span><span class="p">:</span> <span class="n">grad_to_var</span><span class="o">.</span><span class="n">has_key</span><span class="p">(</span><span class="n">n</span><span class="p">),</span>
                         <span class="n">op_desc</span><span class="o">.</span><span class="n">output_arg_names</span><span class="p">()):</span>
        <span class="n">fwd_var</span> <span class="o">=</span> <span class="n">block</span><span class="o">.</span><span class="n">var_recursive</span><span class="p">(</span><span class="n">grad_to_var</span><span class="p">[</span><span class="n">grad_n</span><span class="p">])</span>
        <span class="n">error_clip</span> <span class="o">=</span> <span class="nb">getattr</span><span class="p">(</span><span class="n">fwd_var</span><span class="p">,</span> <span class="s2">&quot;error_clip&quot;</span><span class="p">,</span> <span class="bp">None</span><span class="p">)</span>
        <span class="k">if</span> <span class="n">error_clip</span> <span class="ow">is</span> <span class="ow">not</span> <span class="bp">None</span><span class="p">:</span>
            <span class="n">error_clip</span><span class="o">.</span><span class="n">append_clip_op</span><span class="p">(</span><span class="n">block</span><span class="p">,</span> <span class="n">grad_n</span><span class="p">)</span>
</pre></div>
</div>
<p>This function takes a <code class="docutils literal"><span class="pre">block</span></code> and a <code class="docutils literal"><span class="pre">context</span></code>(which is actually a grad_to_var map) as inputs. It checks each output of the last <code class="docutils literal"><span class="pre">OpDesc</span></code> in the <code class="docutils literal"><span class="pre">block</span></code>. Notice that the last <code class="docutils literal"><span class="pre">OpDesc</span></code> of the <code class="docutils literal"><span class="pre">block</span></code> must be a <code class="docutils literal"><span class="pre">grad_op</span></code> and its outputs must be some forward variables&#8217; gradients. If an output gradient&#8217;s corresponding forward variable has an attribute of <code class="docutils literal"><span class="pre">error_clip</span></code>, <code class="docutils literal"><span class="pre">error_clip_callback</span></code> will call the <code class="docutils literal"><span class="pre">error_clip</span></code>&#8216;s <code class="docutils literal"><span class="pre">append_clip_op</span></code> function to append the required <code class="docutils literal"><span class="pre">clip_op</span></code> into the <code class="docutils literal"><span class="pre">block</span></code>.</p>
</div>
</div>


           </div>
          </div>
          <footer>
  

  <hr/>

  <div role="contentinfo">
    <p>
        &copy; Copyright 2016, PaddlePaddle developers.

    </p>
  </div>
  Built with <a href="http://sphinx-doc.org/">Sphinx</a> using a <a href="https://github.com/snide/sphinx_rtd_theme">theme</a> provided by <a href="https://readthedocs.org">Read the Docs</a>. 

</footer>

        </div>
      </div>

    </section>

  </div>
  


  

    <script type="text/javascript">
        var DOCUMENTATION_OPTIONS = {
            URL_ROOT:'../',
            VERSION:'',
            COLLAPSE_INDEX:false,
            FILE_SUFFIX:'.html',
            HAS_SOURCE:  true,
            SOURCELINK_SUFFIX: ".txt",
        };
    </script>
      <script type="text/javascript" src="../_static/jquery.js"></script>
      <script type="text/javascript" src="../_static/underscore.js"></script>
      <script type="text/javascript" src="../_static/doctools.js"></script>
      <script type="text/javascript" src="../_static/translations.js"></script>
      <script type="text/javascript" src="https://cdn.bootcss.com/mathjax/2.7.0/MathJax.js"></script>
       
  

  
  
    <script type="text/javascript" src="../_static/js/theme.js"></script>
  
  
  <script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/js/bootstrap.min.js" integrity="sha384-Tc5IQib027qvyjSMfHjOMaLkfuWVxZxUPnCJA7l2mCWNIpG9mGCD8wGNIcPD7Txa" crossorigin="anonymous"></script>
  <script src="https://cdn.jsdelivr.net/perfect-scrollbar/0.6.14/js/perfect-scrollbar.jquery.min.js"></script>
  <script src="../_static/js/paddle_doc_init.js"></script> 

</body>
</html>