[GitHub] [incubator-singa] joddiy commented on a change in pull request #489: SINGA-474 selu operator

[GitBox <gi...@apache.org>]

joddiy commented on a change in pull request #489: SINGA-474 selu operator
URL: https://github.com/apache/incubator-singa/pull/489#discussion_r309771204
 
 

 ##########
 File path: python/singa/autograd.py
 ##########
 @@ -357,6 +357,52 @@ def backward(self, dy):
 def relu(x):
     return ReLU()(x)[0]
 
+class SeLU(Operation):
+    def __init__(self,alpha=1.67326,gamma=1.0507):
+        super(SeLU, self).__init__()
+        self.alpha=alpha
+        self.gamma=gamma
+
+    def forward(self, x):
+        """Do forward propgation.
+        Store the x if x requires gradient.
+        Args:
+            x (CTensor): matrix
+        Returns:
+            a CTensor for the result
+        """
+        #y = gamma * (alpha * e^x - alpha) for x <= 0, y = gamma * x for x > 0
+        if training:
+            self.input = x
+        x1 = singa.LTFloat(x, 0.0)
+        x1 = singa.__mul__(x, x1)
+        x1 = singa.MultFloat(singa.SubFloat(singa.MultFloat(singa.Exp(x1),self.alpha),self.alpha),self.gamma)
 
 Review comment:
   can optimize: 
   ```
   singa.MultFloat(singa.SubFloat(singa.Exp(x1), 1.0), self.alpha * self.gamma)
   ```

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