add elu module (#4924)

Co-authored-by: Noneflow-ci-bot <69100618+oneflow-ci-bot@users.noreply.github.com>

docs/source/experimental.rst

@@ -9,6 +9,7 @@ Experimental features
 .. autofunction:: oneflow.experimental.nn.Tanh
 .. autofunction:: oneflow.experimental.tanh
 .. autofunction:: oneflow.experimental.Tensor.tanh
+.. autofunction:: oneflow.experimental.nn.ELU
 .. autofunction:: oneflow.experimental.nn.GELU
 .. autofunction:: oneflow.experimental.gelu
 .. autofunction:: oneflow.experimental.Tensor.gelu

oneflow/python/nn/modules/activation.py

@@ -208,6 +208,55 @@ def tanh_op(x):
     return Tanh()(x)
 
 
+@oneflow_export("nn.ELU")
+@experimental_api
+class ELU(Module):
+    r"""Applies the element-wise function:
+
+    .. math::
+
+        \text{ELU}(x) = \begin{cases}
+				x & \text{ if } x \gt 0  \\
+                \alpha*(exp(x)-1) & \text{ if } x \le 0 \\
+    		    \end{cases}
+
+    Args:
+        alpha: the :math:`\alpha` value for the ELU formulation. Default: 1.0
+        inplace: can optionally do the operation in-place. Default: ``False``
+
+    Shape:
+        - Input: :math:`(N, *)` where `*` means, any number of additional
+          dimensions
+        - Output: :math:`(N, *)`, same shape as the input
+    
+    For example: 
+
+    .. code-block:: python 
+
+        import oneflow.experimental as flow
+        
+        m = flow.nn.ELU()
+        input = flow.randn(2)
+        output = m(input)
+
+    """
+
+    def __init__(self, alpha: float = 1.0, inplace: bool = False):
+        super().__init__()
+        assert inplace == False, f"ELU not support inplace equal true now!"
+        self._op = (
+            flow.builtin_op("elu")
+            .Input("in")
+            .Attr("alpha", alpha)
+            .Output("out")
+            .Build()
+        )
+
+    def forward(self, x):
+        res = self._op(x)[0]
+        return res
+
+
 @oneflow_export("nn.GELU")
 @experimental_api
 class GELU(Module):

oneflow/python/test/modules/test_activation.py

@@ -99,6 +99,28 @@ class TestTanhModule(flow.unittest.TestCase):
         test_case.assertTrue(np.allclose(y.numpy(), z, rtol=1e-4, atol=1e-4))
 
 
+@unittest.skipIf(
+    not flow.unittest.env.eager_execution_enabled(),
+    ".numpy() doesn't work in lazy mode",
+)
+class TestELUModule(flow.unittest.TestCase):
+    def test_elu(test_case):
+        m = flow.nn.ELU()
+        arr = np.random.randn(2, 3, 4, 5)
+        np_out = np.where(arr > 0, arr, 1.0 * (np.exp(arr) - 1))
+        x = flow.Tensor(arr)
+        of_out = m(x)
+        test_case.assertTrue(np.allclose(of_out.numpy(), np_out, rtol=1e-4, atol=1e-4))
+
+    def test_elu_alpha(test_case):
+        m = flow.nn.ELU(alpha=1.2)
+        arr = np.random.randn(2, 3, 4, 5)
+        np_out = np.where(arr > 0, arr, 1.2 * (np.exp(arr) - 1))
+        x = flow.Tensor(arr)
+        of_out = m(x)
+        test_case.assertTrue(np.allclose(of_out.numpy(), np_out, rtol=1e-4, atol=1e-4))
+
+
 @unittest.skipIf(
     not flow.unittest.env.eager_execution_enabled(),
     ".numpy() doesn't work in lazy mode",