loss.py

#   Copyright (c) 2020 PaddlePaddle Authors. All Rights Reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

# TODO: define loss functions of neural network  
import numpy as np
import paddle.fluid as fluid
import paddle.fluid.core as core
import paddle
from .. import functional as F

__all__ = [
    #       'NCELoss',
    'CrossEntropyLoss',
    'MSELoss',
    'L1Loss',
    'NLLLoss',
    'BCELoss',
    'KLDivLoss',
    'MarginRankingLoss',
    'SmoothL1Loss',
]


class CrossEntropyLoss(fluid.dygraph.Layer):
    """
	:alias_main: paddle.nn.CrossEntropyLoss
	:alias: paddle.nn.CrossEntropyLoss,paddle.nn.layer.CrossEntropyLoss,paddle.nn.layer.loss.CrossEntropyLoss

    This operator implements the cross entropy loss function. This OP combines ``LogSoftmax``,
    and ``NLLLoss`` together.

    It is useful when training a classification problem with ``C`` classes.
    If provided, the optional argument ``weight`` should be a 1D Variable assigning
    weight to each of the classes.

    For predictions label, and target label, the loss is calculated as follows.

    .. math::

        loss_j =  -\\text{input[class]} +
        \\log\\left(\\sum_{i=0}^{K}\\exp(\\text{input}_i)\\right), j = 1,..., K

    If weight is not ``None``:

    .. math::

        loss_j =  \\text{weight[class]}(-\\text{input[class]} +
        \\log\\left(\\sum_{i=0}^{K}\\exp(\\text{input}_i)\\right)), j = 1,..., K

    Parameters:
        input (Variable): Input tensor, the data type is float32, float64. Shape is
	    (N, C), where C is number of classes, and if shape is more than 2D, this
	    is (N, C, D1, D2,..., Dk), k >= 1. 
        label (Variable): Label tensor, the data type is int64. Shape is (N), where each 
	    value is 0 <= label[i] <= C-1, and if shape is more than 2D, this is
	    (N, D1, D2,..., Dk), k >= 1.
        weight (Variable, optional): Weight tensor, a manual rescaling weight given
            to each class and the shape is (C). It has the same dimensions as class
	    number and the data type is float32, float64. Default is ``'None'``.
        reduction (str, optional): Indicate how to average the loss by batch_size,
            the candicates are ``'none'`` | ``'mean'`` | ``'sum'``.
            If :attr:`reduction` is ``'mean'``, the reduced mean loss is returned;
            If :attr:`size_average` is ``'sum'``, the reduced sum loss is returned.
            If :attr:`reduction` is ``'none'``, the unreduced loss is returned.
            Default is ``'mean'``.
        ignore_index (int64, optional): Specifies a target value that is ignored
            and does not contribute to the input gradient. Default is ``-100``.

    Returns:
        The tensor variable storing the cross_entropy_loss of input and label.

    Return type: Variable.

    Examples:
        .. code-block:: python

            # declarative mode
            import paddle
            import paddle.fluid as fluid
            import numpy as np

            input = fluid.data(name='input', shape=[5, 100], dtype='float64')
            label = fluid.data(name='label', shape=[5], dtype='int64')
            weight = fluid.data(name='weight', shape=[100], dtype='float64')
            ce_loss = paddle.nn.loss.CrossEntropyLoss(weight=weight, reduction='mean')
            output = ce_loss(input, label)
            place = fluid.CPUPlace()
            exe = fluid.Executor(place)
            exe.run(fluid.default_startup_program())
            input_data = np.random.random([5, 100]).astype("float64")
            label_data = np.random.randint(0, 100, size=(5)).astype(np.int64)
            weight_data = np.random.random([100]).astype("float64")
            output = exe.run(fluid.default_main_program(),
                        feed={"input": input_data, "label": label_data,"weight": weight_data},
                        fetch_list=[output],
                        return_numpy=True)
            print(output)

            # imperative mode
            import paddle.fluid.dygraph as dg
            with dg.guard(place) as g:
                input = dg.to_variable(input_data)
                label = dg.to_variable(label_data)
                weight = dg.to_variable(weight_data)
                ce_loss = paddle.nn.loss.CrossEntropyLoss(weight=weight, reduction='mean')
                output = ce_loss(input, label)
                print(output.numpy())
    """

    def __init__(self, weight=None, reduction='mean', ignore_index=-100):
        super(CrossEntropyLoss, self).__init__()
        self.weight = weight
        self.reduction = reduction
        self.ignore_index = ignore_index

    def forward(self, input, label):
        fluid.data_feeder.check_variable_and_dtype(
            input, 'input', ['float32', 'float64'], 'cross_entropy_loss')
        fluid.data_feeder.check_variable_and_dtype(label, 'label', ['int64'],
                                                   'cross_entropy_loss')

        if self.reduction not in ['sum', 'mean', 'none']:
            raise ValueError(
                "The value of 'reduction' in cross_entropy_loss should be 'sum', 'mean' or"
                " 'none', but received %s, which is not allowed." %
                self.reduction)

        log_softmax = paddle.nn.LogSoftmax()
        log_softmax_out = log_softmax(input)
        if self.weight is not None and not isinstance(self.weight,
                                                      fluid.framework.Variable):
            raise ValueError(
                "The weight' is not a Variable, please convert to Variable.")
        nll_loss = paddle.nn.loss.NLLLoss(
            weight=self.weight,
            reduction=self.reduction,
            ignore_index=self.ignore_index)

        return nll_loss(log_softmax_out, label)


class MSELoss(fluid.dygraph.layers.Layer):
    """
	:alias_main: paddle.nn.MSELoss
	:alias: paddle.nn.MSELoss,paddle.nn.layer.MSELoss,paddle.nn.layer.loss.MSELoss

    **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 same shape.

    Parameters:
        input (Variable): Input tensor, the data type is float32,
        label (Variable): Label tensor, the data type is float32,
        reduction (string, optional): The reduction method for the output,
            could be 'none' | 'mean' | 'sum'.
            If :attr:`reduction` is ``'mean'``, the reduced mean loss is returned. 
            If :attr:`size_average` is ``'sum'``, the reduced sum loss is returned. 
            If :attr:`reduction` is ``'none'``, the unreduced loss is returned. 
            Default is ``'mean'``.

    Returns:
        The tensor variable storing the MSE loss of input and label.

    Return type:
        Variable.

    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.
    The L1Loss layer calculates the L1 Loss of ``input`` and ``label`` as follows.

     If `reduction` set to ``'none'``, the loss is:

    .. math::
        Out = \lvert input - label\rvert

    If `reduction` set to ``'mean'``, the loss is:

    .. math::
        Out = MEAN(\lvert input - label\rvert)

    If `reduction` set to ``'sum'``, the loss is:

    .. math::
        Out = SUM(\lvert input - label\rvert)

    
    Parameters:
        reduction (str, optional): Indicate the reduction to apply to the loss, 
            the candicates are ``'none'`` | ``'mean'`` | ``'sum'``.
            If `reduction` is ``'none'``, the unreduced loss is returned; 
            If `reduction` is ``'mean'``, the reduced mean loss is returned. 
            If `reduction` is ``'sum'``, the reduced sum loss is returned. 
            Default is ``'mean'``.
        name (str, optional): Name for the operation (optional, default is None). For more information, please refer to :ref:`api_guide_Name`.

    Shape:
        input (Tensor): The input tensor. The shapes is [N, *], where N is batch size and `*` means any number of additional dimensions. It's data type should be float32, float64, int32, int64.
        label (Tensor): label. The shapes is [N, *], same shape as ``input`` . It's data type should be float32, float64, int32, int64.
        output (Tensor): The L1 Loss of ``input`` and ``label``. 
            If `reduction` is ``'none'``, the shape of output loss is [N, *], the same as ``input`` .
            If `reduction` is ``'mean'`` or ``'sum'``, the shape of output loss is [1].
            
    Examples:
        .. code-block:: python
            import paddle
            import numpy as np

            paddle.disable_static()
            input_data = np.array([[1.5, 0.8], [0.2, 1.3]]).astype("float32")
            label_data = np.array([[1.7, 1], [0.4, 0.5]]).astype("float32")
            input = paddle.to_variable(input_data)
            label = paddle.to_variable(label_data)

            l1_loss = paddle.nn.loss.L1Loss()
            output = l1_loss(input, label)
            print(output.numpy())  
            # [0.35]

            l1_loss = paddle.nn.loss.L1Loss(reduction='sum')
            output = l1_loss(input, label)
            print(output.numpy())  
            # [1.4]

            l1_loss = paddle.nn.loss.L1Loss(reduction='none')
            output = l1_loss(input, label)
            print(output.numpy())  
            # [[0.20000005 0.19999999]
            # [0.2        0.79999995]]
    """

    def __init__(self, reduction='mean', name=None):
        if reduction not in ['sum', 'mean', 'none']:
            raise ValueError(
                "The value of 'reduction' in L1Loss should be 'sum', 'mean' or 'none', but "
                "received %s, which is not allowed." % reduction)
        super(L1Loss, self).__init__()
        self.reduction = reduction
        self.name = name

    def forward(self, input, label):
        return paddle.nn.functional.l1_loss(
            input, label, self.reduction, name=self.name)


class BCELoss(fluid.dygraph.Layer):
    """
	:alias_main: paddle.nn.BCELoss
	:alias: paddle.nn.BCELoss,paddle.nn.layer.BCELoss,paddle.nn.layer.loss.BCELoss

    This interface is used to construct a callable object of the ``BCELoss`` class.
    The BCELoss layer measures the binary_cross_entropy loss between input predictions 
    and target labels. The binary_cross_entropy loss can be described as:

    If :attr:`weight` is set, the loss is:

    .. math::
        Out = -1 * weight * (label * log(input) + (1 - label) * log(1 - input))
    If :attr:`weight` is None, the loss is:

    .. math::
        Out = -1 * (label * log(input) + (1 - label) * log(1 - input))

    If :attr:`reduction` set to ``'none'``, the unreduced loss is:

    .. math::
        Out = Out
    If :attr:`reduction` set to ``'mean'``, the reduced mean loss is:

    .. math::
        Out = MEAN(Out)
    If :attr:`reduction` set to ``'sum'``, the reduced sum loss is:

    .. math::
        Out = SUM(Out)

    Note that the input predictions always be the output of sigmoid, and the target labels 
    should be numbers between 0 and 1.

    The shape of input predictions and target labels are [N, *], where N is batch_size and `*` 
    means any number of additional dimensions. If ``reduction`` is ``'none'``, the shape of 
    output is scalar, else the shape of output is same as input.

    Parameters:
        weight (Variable, optional): A manual rescaling weight given to the loss of each 
            batch element. If given, has to be a Variable of size nbatch and the data type
            is float32, float64. Default is ``'None'``.
        reduction (str, optional): Indicate how to average the loss by batch_size, 
            the candicates are ``'none'`` | ``'mean'`` | ``'sum'``.
            If :attr:`reduction` is ``'none'``, the unreduced loss is returned;
            If :attr:`reduction` is ``'mean'``, the reduced mean loss is returned; 
            If :attr:`reduction` is ``'sum'``, the summed loss is returned.
            Default is ``'mean'``.

    Returns: 
        A callable object of BCELoss.

    Examples:
        .. code-block:: python

            # declarative mode
            import paddle.fluid as fluid
            import numpy as np
            import paddle
            input = fluid.data(name="input", shape=[3, 1], dtype='float32')
            label = fluid.data(name="label", shape=[3, 1], dtype='float32')
            bce_loss = paddle.nn.loss.BCELoss()
            output = bce_loss(input, label)
            place = fluid.CPUPlace()
            exe = fluid.Executor(place)
            exe.run(fluid.default_startup_program())
    
            input_data = np.array([0.5, 0.6, 0.7]).astype("float32")
            label_data = np.array([1.0, 0.0, 1.0]).astype("float32")
            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([0.65537095], dtype=float32)]
            
            # imperative mode
            import paddle.fluid.dygraph as dg
            with dg.guard(place) as g:
                input = dg.to_variable(input_data)
                label = dg.to_variable(label_data)
                output = bce_loss(input, label)
                print(output.numpy())  # [0.65537095]
    """

    def __init__(self, weight=None, reduction='mean'):
        if reduction not in ['sum', 'mean', 'none']:
            raise ValueError(
                "The value of 'reduction' in bce_loss should be 'sum', 'mean' or 'none', but "
                "received %s, which is not allowed." % reduction)

        super(BCELoss, self).__init__()
        self.weight = weight
        self.reduction = reduction

    def forward(self, input, label):
        dtype = self._helper.input_dtype(input)

        fluid.data_feeder.check_variable_and_dtype(
            input, 'input', ['float32', 'float64'], 'bce_loss')
        fluid.data_feeder.check_variable_and_dtype(
            label, 'label', ['float32', 'float64'], 'bce_loss')

        out = self._helper.create_variable_for_type_inference(dtype=input.dtype)
        self._helper.append_op(
            type='bce_loss',
            inputs={
                'X': [input],
                'Label': [label],
            },
            outputs={'Out': [out]})

        if self.weight is not None:
            if isinstance(self.weight, fluid.framework.Variable):
                w = self.weight
                out = fluid.layers.elementwise_mul(out, w, axis=-1)
            else:
                raise ValueError(
                    "The weight is not a Variable, please convert to Variable.")

        if self.reduction == 'sum':
            return fluid.layers.reduce_sum(out)
        elif self.reduction == 'mean':
            return fluid.layers.reduce_mean(out)
        else:
            return out


class NLLLoss(fluid.dygraph.Layer):
    """
	:alias_main: paddle.nn.NLLLoss
	:alias: paddle.nn.NLLLoss,paddle.nn.layer.NLLLoss,paddle.nn.layer.loss.NLLLoss

    This class accepts input and target label and returns negative log likelihood
    cross error. It is useful to train a classification problem with C classes.
     
    The input for the loss is epected to contain log-probabilities of
    each classes. It has to be a Tensor of size either (batch_size, C) or
    (batch_size, C, d1, d2, ..., dK) with K >= 1 for the K-dimensional case.
    The label for the loss should be a class index in the range [0, C-1]
    where C is the number of classes. If ignore_index is specified, the
    specified target value does not contribute to the input gradient.
    
    If the optional argument `weight` is provided, it should be a 1D Tensor
    assigning weight to each of the classed. This is particularly useful
    when you have an unbalanced training set.
 
    The loss is calculated as follows.
    The unreduced (i.e. with :attr:`reduction` set to ``'none'``) loss can be described as:

    .. math::
        \ell(x, y) = L = \{l_1,\dots,l_N\}^\\top, \quad
        l_n = - w_{y_n} x_{n,y_n}, \quad
        w_{c} = \\text{weight}[c] \cdot \mathbb{1}\{c \\not= \\text{ignore\\_index}\},

    where :math:`N` is the batch size. If :attr:`reduction` is not ``'none'``
    (default ``'mean'``), then

    .. math::
        \ell(x, y) = \\begin{cases}
            \\sum_{n=1}^N \\frac{1}{\\sum_{n=1}^N w_{y_n}} l_n, &
            \\text{if reduction} = \\text{'mean';}\\\\
            \\sum_{n=1}^N l_n,  &
            \\text{if reduction} = \\text{'sum'.}
        \\end{cases}

    Parameters:
        weight (Tensor, optional): Weight tensor, a manual rescaling weight given
            to each class. If given, it has to be a 1D Tensor whose size is `[C, ]`. Otherwise,
            it treated as if having all ones. the data type is 
            float32, float64, Default is ``'None'``.
        ignore_index (int64, optional): Specifies a target value that is ignored
            and does not contribute to the input gradient.
        reduction (str, optional): Indicate how to average the loss, 
            the candicates are ``'none'`` | ``'mean'`` | ``'sum'``.
            If `reduction` is ``'mean'``, the reduced mean loss is returned;
            if `reduction` is ``'sum'``, the reduced sum loss is returned;
            if `reduction` is ``'none'``, no reduction will be apllied.
            Default is ``'mean'``.
         name (str, optional): Name for the operation (optional, default is None).
             For more information, please refer to :ref:`api_guide_Name`.

    Shape:
        input (Tensor): Input tensor, the shape is :math:`[N, C]`, `C` is the number of classes.
            But in K-dimension situation, the shape is :math:`[N, C, d_1, d_2, ..., d_K]`.
            The data type is float32, float64.
        label (Tensor): Label tensor, the shape is :math:`[N,]` or :math:`[N, d_1, d_2, ..., d_K]`.
            The data type is int64.
        output (Tensor): the `negative log likelihood loss` between input `x` and `label`.
            If `reduction` is `'none'`, the shape is `[N, *]`.
            If `reduction` is `'sum'` or `'mean'`, the shape is `[1]`.

    Examples:
        .. code-block:: python

                import paddle
                import numpy as np

                nll_loss = paddle.nn.layer.NLLLoss()
                log_softmax = paddle.nn.LogSoftmax(axis=1)

                input_np = np.array([[0.88103855, 0.9908683 , 0.6226845 ],
                                 [0.53331435, 0.07999352, 0.8549948 ],
                                 [0.25879037, 0.39530203, 0.698465  ],
                                 [0.73427284, 0.63575995, 0.18827209],
                                 [0.05689114, 0.0862954 , 0.6325046 ]]).astype(np.float32)
                label_np = np.array([0, 2, 1, 1, 0]).astype(np.int64)

                place = paddle.CPUPlace()
                paddle.disable_static(place)
                input = paddle.to_variable(input_np)
                log_out = log_softmax(input)
                label = paddle.to_variable(label_np)
                result = nll_loss(log_out, label)
                print(result.numpy()) # [1.0720209]

    """

    def __init__(self,
                 weight=None,
                 ignore_index=-100,
                 reduction='mean',
                 name=None):
        if reduction not in ['sum', 'mean', 'none']:
            raise ValueError(
                "The value of 'reduction' in nll_loss should be 'sum', 'mean' or "
                "'none', but received %s, which is not allowed." % reduction)
        super(NLLLoss, self).__init__()
        self._weight = weight
        self._ignore_index = ignore_index
        self._reduction = reduction
        self._name = name

    def forward(self, input, label):
        return F.nll_loss(
            input,
            label,
            weight=self._weight,
            ignore_index=self._ignore_index,
            reduction=self._reduction,
            name=self._name)


class KLDivLoss(fluid.dygraph.Layer):
    """
    This interface calculates the Kullback-Leibler divergence loss
    between Input(X) and Input(Target). Notes that Input(X) is the
    log-probability and Input(Target) is the probability.

    KL divergence loss is calculated as follows:

    $$l(x, y) = y * (\log(y) - x)$$

    Parameters:
        reduction (str, optional): Indicate how to average the loss, 
            the candicates are ``'none'`` | ``'mean'`` | ``'sum'``.
            If :attr:`reduction` is ``'mean'``, the reduced mean loss is returned; 
            Default is ``'mean'``.

    Shape:
      - input: (N, *) where * means, any number of additional dimensions.
      - label: (N, *), same shape as input
      - output: tensor with shape: (1) by default.


    Examples:
        .. code-block:: python

            import paddle
            import numpy as np
            import paddle.nn as nn
            
            paddle.enable_imperative()

            shape = (5, 20)
            x = np.random.uniform(-10, 10, shape).astype('float32')
            target = np.random.uniform(-10, 10, shape).astype('float32')

            # 'batchmean' reduction, loss shape will be [N]
            kldiv_criterion = nn.KLDivLoss(reduction='batchmean')
            pred_loss = kldiv_criterion(paddle.to_variable(x),
                                        paddle.to_variable(target))
            # shape=[5]
            
            # 'mean' reduction, loss shape will be [1]
            kldiv_criterion = nn.KLDivLoss(reduction='mean')
            pred_loss = kldiv_criterion(paddle.to_variable(x),
                                        paddle.to_variable(target))
            # shape=[1]

            # 'sum' reduction, loss shape will be [1]
            kldiv_criterion = nn.KLDivLoss(reduction='sum')
            pred_loss = kldiv_criterion(paddle.to_variable(x),
                                        paddle.to_variable(target))
            # shape=[1]

            # 'none' reduction, loss shape is same with X shape
            kldiv_criterion = nn.KLDivLoss(reduction='none')
            pred_loss = kldiv_criterion(paddle.to_variable(x),
                                        paddle.to_variable(target))
            # shape=[5, 20]
    """

    def __init__(self, reduction='mean'):
        super(KLDivLoss, self).__init__()
        self.reduction = reduction

    def forward(self, input, label):
        out = paddle.nn.functional.kl_div(input, label, self.reduction)
        return out


class MarginRankingLoss(fluid.dygraph.Layer):
    """

    This interface is used to construct a callable object of the ``MarginRankingLoss`` class.
    The MarginRankingLoss layer calculates the margin rank loss between the input, other and label 
    , use the math function as follows.

    .. math:: 
        margin\_rank\_loss = max(0, -label * (input - other) + margin)

    If :attr:`reduction` set to ``'mean'``, the reduced mean loss is:

    .. math::
        Out = MEAN(margin\_rank\_loss)

    If :attr:`reduction` set to ``'sum'``, the reduced sum loss is:

    .. math::
        Out = SUM(margin\_rank\_loss)

    If :attr:`reduction` set to ``'none'``, just return the origin ``margin_rank_loss``.

    Parameters:
        margin (float, optional): The margin value to add, default value is 0;
        reduction (str, optional): Indicate the reduction to apply to the loss, the candicates are ``'none'``, ``'mean'``, ``'sum'``.If :attr:`reduction` is ``'none'``, the unreduced loss is returned; If :attr:`reduction` is ``'mean'``, the reduced mean loss is returned. If :attr:`reduction` is ``'sum'``, the reduced sum loss is returned. Default is ``'mean'``.
        name (str, optional): Name for the operation (optional, default is None). For more information, please refer to :ref:`api_guide_Name`.

    Shape: 
        input: N-D Tensor, the shape is [N, *], N is batch size and `*` means any number of additional dimensions., available dtype is float32, float64.
        other: N-D Tensor, `other` have the same shape and dtype as `input`.
        label: N-D Tensor, label have the same shape and dtype as `input`.
        output: If :attr:`reduction` is ``'mean'`` or ``'sum'`` , the out shape is :math:`[1]`, otherwise the shape is the same as `input` .The same dtype as input tensor.

    Returns:
        A callable object of MarginRankingLoss.

    Examples:

        .. code-block:: python

            import numpy as np 
            import paddle 
            
            paddle.disable_static()
             
            input = paddle.to_variable(np.array([[1, 2], [3, 4]]).astype("float32"))
            other = paddle.to_variable(np.array([[2, 1], [2, 4]]).astype("float32"))
            label = paddle.to_variable(np.array([[1, -1], [-1, -1]]).astype("float32"))
            margin_rank_loss = paddle.nn.MarginRankingLoss()
            loss = margin_rank_loss(input, other, label) 
            print(loss.numpy()) # [0.75]
    """

    def __init__(self, margin=0.0, reduction='mean', name=None):
        if reduction not in ['sum', 'mean', 'none']:
            raise ValueError(
                "The value of 'reduction' in MarginRankingLoss should be 'sum', 'mean' or 'none', but "
                "received %s, which is not allowed." % reduction)
        super(MarginRankingLoss, self).__init__()
        self.margin = margin
        self.reduction = reduction
        self.name = name

    def forward(self, input, other, label):
        out = paddle.nn.functional.margin_ranking_loss(
            input, other, label, self.margin, self.reduction, self.name)
        return out


class SmoothL1Loss(fluid.dygraph.Layer):
    """
    This operator calculates smooth_l1_loss. Creates a criterion that uses a squared
    term if the absolute element-wise error falls below 1 and an L1 term otherwise.
    In some cases it can prevent exploding gradients and it is more robust and less
    sensitivity to outliers. Also known as the Huber loss:

    .. math::

         loss(x,y)=\\frac{1}{n}\\sum_{i}z_i

    where z_i is given by:

    .. math::

         \\mathop{z_i}=\\left\\{\\begin{array}{rcl}
        0.5(x_i - y_i)^2 & & {if |x_i - y_i| < delta} \\\\
        delta * |x_i - y_i| - 0.5 * delta^2 & & {otherwise}
        \\end{array} \\right.

    Parameters:
        reduction (str, optional): Indicate how to average the loss by batch_size,
            the candicates are ``'none'`` | ``'mean'`` | ``'sum'``.
            If :attr:`reduction` is ``'mean'``, the reduced mean loss is returned;
            If :attr:`reduction` is ``'sum'``, the reduced sum loss is returned.
            If :attr:`reduction` is ``'none'``, the unreduced loss is returned.
            Default is ``'mean'``.
        delta (float, optional): Specifies the hyperparameter delta to be used. 
            The value determines how large the errors need to be to use L1. Errors
            smaller than delta are minimized with L2. Parameter is ignored for
            negative/zero values. Default = 1.0
        name (str, optional): Name for the operation (optional, default is
            None). For more information, please refer to :ref:`api_guide_Name`.

    Call Parameters:
        input (Tensor): Input tensor, the data type is float32 or float64. Shape is
            (N, C), where C is number of classes, and if shape is more than 2D, this
            is (N, C, D1, D2,..., Dk), k >= 1.
        label (Tensor): Label tensor, the data type is float32 or float64. The shape of label
            is the same as the shape of input.

    Returns:
        The tensor variable storing the smooth_l1_loss of input and label.

    Return type: Tensor.

    Examples:
        .. code-block:: python

            import paddle
            import numpy as np
            paddle.disable_static()
            input_data = np.random.rand(3,3).astype("float32")
            label_data = np.random.rand(3,3).astype("float32")
            input = paddle.to_tensor(input_data)
            label = paddle.to_tensor(label_data)
            loss = paddle.nn.SmoothL1Loss()
            output = loss(input, label)
            print(output.numpy())
    """

    def __init__(self, reduction='mean', delta=1.0, name=None):
        super(SmoothL1Loss, self).__init__()
        self.reduction = reduction
        self.delta = delta
        self.name = name

    def forward(self, input, label):
        return F.smooth_l1_loss(
            input,
            label,
            reduction=self.reduction,
            delta=self.delta,
            name=self.name)