Added Sqeeuze/Excite and BatchNorm recipes.

Author: vahidk

README.md

@@ -24,7 +24,8 @@ Table of Contents
     - [KL-Divergence](#kld)
     - [Make parallel](#make_parallel)
     - [Leaky Relu](#leaky_relu)
-
+    - [Batch normalization](#batch_norm)
+    - [Squeeze and excitation](#squeeze_excite)
 ---
 
 _We aim to gradually expand this series by adding new articles and keep the content up to date with the latest releases of TensorFlow API. If you have suggestions on how to improve this series or find the explanations ambiguous, feel free to create an issue, send patches, or reach out by email._
@@ -1409,3 +1410,74 @@ def leaky_relu(tensor, alpha=0.1):
     """Computes the leaky rectified linear activation."""
     return tf.maximum(x, alpha * x)
 ```
+
+## Batch normalization <a name="batch_norm"></a>
+```python
+def batch_normalization(tensor, training=False, epsilon=0.001, momentum=0.9, 
+                        fused_batch_norm=False, name=None):
+  """Performs batch normalization on given 4-D tensor.
+  
+  The features are assumed to be in NHWC format. Noe that you need to 
+  run UPDATE_OPS in order for this function to perform correctly, e.g.:
+
+  with tf.control_dependencies(tf.get_collection(tf.GraphKeys.UPDATE_OPS)):
+    train_op = optimizer.minimize(loss)
+  """
+  with tf.variable_scope(name, default_name="batch_normalization"):
+    channels = tensor.shape.as_list()[-1]
+    axes = list(range(tensor.shape.ndims - 1))
+
+    beta = tf.get_variable(
+      'beta', channels, initializer=tf.zeros_initializer())
+    gamma = tf.get_variable(
+      'gamma', channels, initializer=tf.ones_initializer())
+
+    avg_mean = tf.get_variable(
+      "avg_mean", channels, initializer=tf.zeros_initializer(),
+      trainable=False)
+    avg_variance = tf.get_variable(
+      "avg_variance", channels, initializer=tf.ones_initializer(),
+      trainable=False)
+
+    if training:
+      if fused_batch_norm:
+        mean, variance = None, None
+      else:
+        mean, variance = tf.nn.moments(tensor, axes=axes)
+    else:
+      mean, variance = avg_mean, avg_variance
+   
+    if fused_batch_norm:
+      tensor, mean, variance = tf.nn.fused_batch_norm(
+        tensor, scale=gamma, offset=beta, mean=mean, variance=variance, 
+        epsilon=epsilon, is_training=training)
+    else:
+      tensor = tf.nn.batch_normalization(
+        tensor, mean, variance, beta, gamma, epsilon)
+
+    if training:
+      update_mean = tf.assign(
+        avg_mean, avg_mean * momentum + mean * (1.0 - momentum))
+      update_variance = tf.assign(
+        avg_variance, avg_variance * momentum + variance * (1.0 - momentum))
+
+      tf.add_to_collection(tf.GraphKeys.UPDATE_OPS, update_mean)
+      tf.add_to_collection(tf.GraphKeys.UPDATE_OPS, update_variance)
+
+  return tensor
+```
+
+## Squeeze and excitation <a name="squeeze_excite"></a>
+```python
+def squeeze_and_excite(tensor, ratio):
+  """Squeeze and excite layer."""
+  original = tensor
+  units = tensor.shape.as_list()[-1]
+  tensor = tf.reduce_mean(tensor, [1, 2], keep_dims=True)
+  tensor = tf.layers.dense(tensor, units / ratio, use_bias=False)
+  tensor = tf.nn.relu(tensor)
+  tensor = tf.layers.dense(tensor, units, use_bias=False)
+  tensor = tf.nn.sigmoid(tensor)
+  tensor = original * tensor
+  return tensor
+```