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#
# 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',
    'MarginRankingLoss'
]


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 ``x`` and ``label`` as follows.

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

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

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

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

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

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

    
    Parameters:
        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:
        x (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 ``x`` . It's data type should be float32, float64, int32, int64.
        output (Tensor): The L1 Loss of ``x`` and ``label``. 
            If :attr:`reduction` is ``'none'``, the shape of output loss is [N, *], the same as ``x`` .
            If :attr:`reduction` is ``'mean'`` or ``'sum'``, the shape of output loss is [1], which means the output is a scalar.
            
    Examples:
        .. code-block:: python
            import paddle
            import numpy as np

            paddle.disable_static()
            x_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")
            x = paddle.to_variable(x_data)
            label = paddle.to_variable(label_data)

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

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

            l1_loss = paddle.nn.loss.L1Loss(reduction='none')
            output = l1_loss(x, 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, x, label):
        return paddle.nn.functional.l1_loss(
            x, 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 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 target 
    , use the math function as follows.

    .. math:: 
        margin\_rank\_loss = max(0, -target * (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`.
        target: N-D Tensor, target have the same shape and dtype as `input`.
        out: 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"))
            target = paddle.to_variable(np.array([[1, -1], [-1, -1]]).astype("float32"))
            margin_rank_loss = paddle.nn.MarginRankingLoss()
            loss = margin_rank_loss(input, other, target) 
            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 L1Loss 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, target):
        out = paddle.nn.functional.margin_ranking_loss(
            input, other, target, self.margin, self.reduction, self.name)
        return out
