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From GitBox <...@apache.org>
Subject [GitHub] [incubator-singa] joddiy commented on a change in pull request #480: SINGA-474 ELU operator
Date Thu, 01 Aug 2019 15:31:40 GMT
joddiy commented on a change in pull request #480: SINGA-474 ELU operator
URL: https://github.com/apache/incubator-singa/pull/480#discussion_r309702428
 
 

 ##########
 File path: python/singa/autograd.py
 ##########
 @@ -358,6 +358,48 @@ def relu(x):
     return ReLU()(x)[0]
 
 
+class Elu(Operation):
+    def __init__(self,alpha=1):
+        super(Elu, self).__init__()
+        self.alpha=alpha
+
+    def forward(self, x):
+        """Do forward propgation.
+        Store the x if requires gradient.
+        Args:
+            x (CTensor): matrix
+        Returns:
+            a CTensor for the result
+        """
+        #f(x) = alpha * (exp(x) - 1.) for x < 0, f(x) = x for x >= 0
+        if training:
+            self.input = x
+        x1 = singa.LTFloat(x, 0.0)
+        x1 = singa.__mul__(x, x1)
+        x1 = singa.SubFloat(singa.Exp(x1),self.alpha)
+        x2 = singa.ReLU(x)
+        x1 = singa.__add__(x1, x2)
+        return x1
+
+    def backward(self, dy):
+        """
+        Args:
+            dy (CTensor): data for the dL / dy, L is the loss
+        Returns:
+            a tuple for dx
+        """
+        dx1mask = singa.LTFloat(self.input, 0.0)
+        dx1 = singa.MultFloat(singa.Exp(self.input), self.alpha)
 
 Review comment:
   is this formula correct?

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