[Cherry-pick Release 2.0] Add `paddle.nn.loss.MSELoss` (#23981)

* Add `paddle.nn.loss.MSELoss`

test=develop

* Move to `nn/layer/loss.py`

test=develop

* Fix dygraph

test=develop

* Add test

test=develop

* Increase numel in test

test=develop

* Add test for input with different dimensions

test=develop

python/paddle/fluid/tests/unittests/test_mse_loss.py

@@ -16,7 +16,7 @@ from __future__ import print_function
 
 import unittest
 import numpy as np
-import sys
+import paddle
 import paddle.fluid.core as core
 import paddle.fluid as fluid
 import paddle.fluid.layers as layers
@@ -64,5 +64,118 @@ class TestMseInvalidInput(unittest.TestCase):
         self.assertRaises(TypeError, test_invalid_label)
 
 
+class TestNNMseLoss(unittest.TestCase):
+    def test_NNMseLoss_mean(self):
+        for dim in [[10, 10], [2, 10, 10], [3, 3, 10, 10]]:
+            input_np = np.random.uniform(0.1, 0.5, dim).astype("float32")
+            label_np = np.random.uniform(0.1, 0.5, dim).astype("float32")
+            prog = fluid.Program()
+            startup_prog = fluid.Program()
+            place = fluid.CUDAPlace(0) if fluid.core.is_compiled_with_cuda(
+            ) else fluid.CPUPlace()
+            with fluid.program_guard(prog, startup_prog):
+                input = fluid.layers.data(
+                    name='input', shape=dim, dtype='float32')
+                label = fluid.layers.data(
+                    name='label', shape=dim, dtype='float32')
+                mse_loss = paddle.nn.loss.MSELoss()
+                ret = mse_loss(input, label)
+
+                exe = fluid.Executor(place)
+                static_result = exe.run(
+                    prog,
+                    feed={"input": input_np,
+                          "label": label_np},
+                    fetch_list=[ret])
+
+            with fluid.dygraph.guard():
+                mse_loss = paddle.nn.loss.MSELoss()
+                dy_ret = mse_loss(
+                    fluid.dygraph.to_variable(input_np),
+                    fluid.dygraph.to_variable(label_np))
+                dy_result = dy_ret.numpy()
+
+            sub = input_np - label_np
+            expected = np.mean(sub * sub)
+            self.assertTrue(np.allclose(static_result, expected))
+            self.assertTrue(np.allclose(static_result, dy_result))
+            self.assertTrue(np.allclose(dy_result, expected))
+            self.assertTrue(dy_result.shape, [1])
+
+    def test_NNMseLoss_sum(self):
+        for dim in [[10, 10], [2, 10, 10], [3, 3, 10, 10]]:
+            input_np = np.random.uniform(0.1, 0.5, dim).astype("float32")
+            label_np = np.random.uniform(0.1, 0.5, dim).astype("float32")
+            prog = fluid.Program()
+            startup_prog = fluid.Program()
+            place = fluid.CUDAPlace(0) if fluid.core.is_compiled_with_cuda(
+            ) else fluid.CPUPlace()
+            with fluid.program_guard(prog, startup_prog):
+                input = fluid.layers.data(
+                    name='input', shape=dim, dtype='float32')
+                label = fluid.layers.data(
+                    name='label', shape=dim, dtype='float32')
+                mse_loss = paddle.nn.loss.MSELoss(reduction='sum')
+                ret = mse_loss(input, label)
+
+                exe = fluid.Executor(place)
+                static_result = exe.run(
+                    prog,
+                    feed={"input": input_np,
+                          "label": label_np},
+                    fetch_list=[ret])
+
+            with fluid.dygraph.guard():
+                mse_loss = paddle.nn.loss.MSELoss(reduction='sum')
+                dy_ret = mse_loss(
+                    fluid.dygraph.to_variable(input_np),
+                    fluid.dygraph.to_variable(label_np))
+                dy_result = dy_ret.numpy()
+
+            sub = input_np - label_np
+            expected = np.sum(sub * sub)
+            self.assertTrue(np.allclose(static_result, expected))
+            self.assertTrue(np.allclose(static_result, dy_result))
+            self.assertTrue(np.allclose(dy_result, expected))
+            self.assertTrue(dy_result.shape, [1])
+
+    def test_NNMseLoss_none(self):
+        for dim in [[10, 10], [2, 10, 10], [3, 3, 10, 10]]:
+            input_np = np.random.uniform(0.1, 0.5, dim).astype("float32")
+            label_np = np.random.uniform(0.1, 0.5, dim).astype("float32")
+            prog = fluid.Program()
+            startup_prog = fluid.Program()
+            place = fluid.CUDAPlace(0) if fluid.core.is_compiled_with_cuda(
+            ) else fluid.CPUPlace()
+            with fluid.program_guard(prog, startup_prog):
+                input = fluid.layers.data(
+                    name='input', shape=dim, dtype='float32')
+                label = fluid.layers.data(
+                    name='label', shape=dim, dtype='float32')
+                mse_loss = paddle.nn.loss.MSELoss(reduction='none')
+                ret = mse_loss(input, label)
+
+                exe = fluid.Executor(place)
+                static_result = exe.run(
+                    prog,
+                    feed={"input": input_np,
+                          "label": label_np},
+                    fetch_list=[ret])
+
+            with fluid.dygraph.guard():
+                mse_loss = paddle.nn.loss.MSELoss(reduction='none')
+                dy_ret = mse_loss(
+                    fluid.dygraph.to_variable(input_np),
+                    fluid.dygraph.to_variable(label_np))
+                dy_result = dy_ret.numpy()
+
+            sub = input_np - label_np
+            expected = (sub * sub)
+            self.assertTrue(np.allclose(static_result, expected))
+            self.assertTrue(np.allclose(static_result, dy_result))
+            self.assertTrue(np.allclose(dy_result, expected))
+            self.assertTrue(dy_result.shape, [1])
+
+
 if __name__ == "__main__":
     unittest.main()

python/paddle/nn/layer/loss.py

@@ -17,7 +17,7 @@ import paddle.fluid as fluid
 __all__ = [
     #'NCELoss',
     'CrossEntropyLoss',
-    #    'MSELoss',
+    'MSELoss',
     'L1Loss',
     #    'NLLLoss',
     'BCELoss'
@@ -135,6 +135,97 @@ class CrossEntropyLoss(fluid.dygraph.Layer):
             return out
 
 
+class MSELoss(fluid.dygraph.layers.Layer):
+    """
+    **Mean Square Error Loss**
+    Computes the mean square error (squared L2 norm) of given input and label.
+
+    If :attr:`reduction` is set to ``'none'``, loss is calculated as:
+
+    .. math::
+        Out = (input - label)^2
+
+    If :attr:`reduction` is set to ``'mean'``, loss is calculated as:
+
+    .. math::
+        Out = \operatorname{mean}((input - label)^2)
+
+    If :attr:`reduction` is set to ``'sum'``, loss is calculated as:
+
+    .. math::
+        Out = \operatorname{sum}((input - label)^2)
+
+    where `input` and `label` are `float32` tensors of arbitrary shapes.
+
+    Parameters:
+        reduction (string, optional): The reduction method for the output,
+            could be 'none' | 'mean' | 'sum'.
+            'none': no reduction will be applied
+            'mean': the output will be averaged
+            'sum': the output will be summed
+
+    Examples:
+        .. code-block:: python
+        import numpy as np
+        import paddle
+        from paddle import fluid
+        import paddle.fluid.dygraph as dg
+
+        mse_loss = paddle.nn.loss.MSELoss()
+        input = fluid.data(name="input", shape=[1])
+        label = fluid.data(name="label", shape=[1])
+        place = fluid.CPUPlace()
+        input_data = np.array([1.5]).astype("float32")
+        label_data = np.array([1.7]).astype("float32")
+
+        # declarative mode
+        output = mse_loss(input,label)
+        exe = fluid.Executor(place)
+        exe.run(fluid.default_startup_program())
+        output_data = exe.run(
+            fluid.default_main_program(),
+            feed={"input":input_data, "label":label_data},
+            fetch_list=[output],
+            return_numpy=True)
+        print(output_data)
+        # [array([0.04000002], dtype=float32)]
+
+        # imperative mode
+        with dg.guard(place) as g:
+            input = dg.to_variable(input_data)
+            label = dg.to_variable(label_data)
+            output = mse_loss(input, label)
+            print(output.numpy())
+            # [0.04000002]
+    """
+
+    def __init__(self, reduction='mean'):
+        super(MSELoss, self).__init__()
+        if reduction not in ['sum', 'mean', 'none']:
+            raise ValueError(
+                "'reduction' in 'MSELoss' should be 'sum', 'mean' or 'none', "
+                "but received {}.".format(reduction))
+        self.reduction = reduction
+
+    def forward(self, input, label):
+        if not fluid.framework.in_dygraph_mode():
+            fluid.data_feeder.check_variable_and_dtype(input, 'input',
+                                                       ['float32'], 'MSELoss')
+            fluid.data_feeder.check_variable_and_dtype(label, 'label',
+                                                       ['float32'], 'MSELoss')
+
+        square_out = fluid.layers.square(
+            fluid.layers.elementwise_sub(input, label))
+        if self.reduction == 'none':
+            return square_out
+
+        reduce_op = 'reduce_mean'
+        if self.reduction == 'sum':
+            reduce_op = 'reduce_sum'
+
+        return getattr(fluid.layers, reduce_op)(square_out)
+
+
 class L1Loss(fluid.dygraph.Layer):
     """
     This interface is used to construct a callable object of the ``L1Loss`` class.