[BUGFIX] fix ELU function will appear nan when calculating the gradient

python/mxnet/gluon/nn/activations.py

@@ -153,12 +153,13 @@ class ELU(HybridBlock):
     Outputs:
         - **out**: output tensor with the same shape as `data`.
     """
+
     def __init__(self, alpha=1.0, **kwargs):
         super(ELU, self).__init__(**kwargs)
         self._alpha = alpha
 
     def hybrid_forward(self, F, x):
-        return F.where(x > 0, x, self._alpha * (F.exp(x) - 1.0))
+        return F.LeakyReLU(x, act_type='elu', slope=self._alpha)
 
 
 class SELU(HybridBlock):

tests/python/unittest/test_gluon.py

@@ -1180,7 +1180,7 @@ def swish_test(x):
     elu = mx.gluon.nn.ELU()
     def elu_test(x):
         def elu(x):
-            return 1.0 * (mx.nd.exp(x) - 1) if x < 0 else x
+            return mx.nd.expm1(x) if x <= 0.0 else x
         return [elu(x_i) for x_i in x]
 
     for test_point, ref_point in zip(elu_test(point_to_validate), elu(point_to_validate)):