Create tf.nn.lrn.md

tensorflow2fluid/doc/tf.nn.lrn.md

+
+## tf.nn.lrn
+
+### [tf.nn.lrn](https://www.tensorflow.org/api_docs/python/tf/nn/local_response_normalization)
+
+```python
+tf.nn.local_response_normalization(
+    input,
+    depth_radius=5,
+    bias=1,
+    alpha=1,
+    beta=0.5,
+    name=None
+)
+```
+
+### [paddle.fluid.layers.lrn](http://paddlepaddle.org/documentation/docs/zh/1.3/api_cn/layers_cn.html#paddle.fluid.layers.lrn)
+
+```python
+paddle.fluid.layers.lrn(
+    input, 
+    n=5, 
+    k=1.0, 
+    alpha=0.0001, 
+    beta=0.75, 
+    name=None
+)
+```
+
+### 功能差异
+
+#### 计算方式
+
+TensorFlow：计算公式如下所示，
+$$output(i,x,y)=input(i,x,y)/(k+\alpha\sum_{j=max(0,i-depth_radius)}^{min(C,i+depth_radius+1)}{input(j,x,y)^2})^\beta$$ 
+PaddlePaddle：计算公式如下所示，
+
+
+
+### 代码示例
+```
+# x是shape为[3,2]的张量
+
+# out同样是shape[3,2]的张量，axis设置为1，表示将x中每个行向量做归一化
+out = fluid.layers.l2_normalize(x, axis=1)
+```