Reconstruct module files (#5251)

* reconstruct modules and aligin torch

* format

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

oneflow/python/nn/modules/activation.py

@@ -40,6 +40,67 @@ def _softmax_need_transpose(x, axis):
     return need_transpose, permute
 
 
+@oneflow_export("nn.PReLU")
+@experimental_api
+class PReLU(Module):
+    """Applies the element-wise function:
+
+    .. math::
+        PReLU(x) = \max(0,x) + a * \min(0,x)
+
+    Here :math:`a` is a learnable parameter. When called without arguments, `nn.PReLU()` uses a single
+    parameter :math:`a` across all input channels. If called with `nn.PReLU(nChannels)`,
+    a separate :math:`a` is used for each input channel.
+
+
+    .. note::
+        weight decay should not be used when learning :math:`a` for good performance.
+
+    .. note::
+        Channel dim is the 2nd dim of input. When input has dims < 2, then there is
+        no channel dim and the number of channels = 1.
+
+    Args:
+        num_parameters (int): number of :math:`a` to learn.
+            Although it takes an int as input, there is only two values are legitimate:
+            1, or the number of channels at input. Default: 1
+        init (float): the initial value of :math:`a`. Default: 0.25
+
+    Shape:
+        - Input: :math:`(N, *)` where `*` means, any number of additional
+          dimensions
+        - Output: :math:`(N, *)`, same shape as the input
+
+    Attr:
+        - weight (Tensor): the learnable weights of shape (:attr:`num_parameters`).
+
+    .. code-block:: python
+
+        >>> import numpy as np
+        >>> import oneflow.experimental as flow
+        >>> flow.enable_eager_execution()
+
+        >>> m = flow.nn.PReLU()
+        >>> input = flow.Tensor(np.asarray([[[[1, -2], [3, 4]]]]), dtype=flow.float32)
+        >>> print(m(input).numpy())
+        [[[[ 1.  -0.5]
+           [ 3.   4. ]]]]
+
+    """
+
+    def __init__(self, num_parameters: int = 1, init: float = 0.25) -> None:
+        super().__init__()
+        self.num_parameters = num_parameters
+        self.weight = flow.nn.Parameter(flow.Tensor(num_parameters, 1, 1).fill_(init))
+        self.op = flow.builtin_op("prelu").Input("x").Input("alpha").Output("y").Build()
+
+    def forward(self, x):
+        assert (
+            self.num_parameters == 1 or self.num_parameters == x.shape[1]
+        ), f"num_parameters in prelu must be 1 or {x.shape[1]}"
+        return self.op(x, self.weight)[0]
+
+
 @oneflow_export("nn.ReLU")
 @experimental_api
 class ReLU(Module):