# Source code for mindspore.nn.metrics.loss

# Copyright 2020-2021 Huawei Technologies Co., Ltd
#
# 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
#
#
# 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.
# ============================================================================
"""Loss for evaluation"""
from __future__ import absolute_import

from .metric import Metric, rearrange_inputs

[文档]class Loss(Metric):
r"""
Calculates the average of the loss. If method 'update' is called every :math:n iterations, the result of
evaluation will be:

.. math::
loss = \frac{\sum_{k=1}^{n}loss_k}{n}

Supported Platforms:
Ascend GPU CPU

Examples:
>>> import numpy as np
>>> import mindspore
>>> from mindspore import nn, Tensor
>>>
>>> x = Tensor(np.array(0.2), mindspore.float32)
>>> loss = nn.Loss()
>>> loss.clear()
>>> loss.update(x)
>>> result = loss.eval()
>>> print(result)
0.20000000298023224
"""
def __init__(self):
super(Loss, self).__init__()
self.clear()

[文档]    def clear(self):
"""Clears the internal evaluation result."""
self._sum_loss = 0
self._total_num = 0

[文档]    @rearrange_inputs
def update(self, *inputs):
"""
Updates the internal evaluation result.

Args:
inputs: Inputs contain only one element, the element is loss. The dimension of
loss must be 0 or 1.

Raises:
ValueError: If the length of inputs is not 1.
ValueError: If the dimension of loss is not 1 or 0.
"""
if len(inputs) != 1:
raise ValueError("For 'Loss.update', it needs 1 input (loss), but got {}".format(len(inputs)))

loss = self._convert_data(inputs[0])

if loss.ndim == 0:
loss = loss.reshape(1)

if loss.ndim != 1:
raise ValueError("For 'Loss.update', the dimension of your input (loss) must be 1, "
"but got {}.".format(loss.ndim))

loss = loss.mean(-1)
self._sum_loss += loss
self._total_num += 1

[文档]    def eval(self):
"""
Calculates the average of the loss.

Returns:
numpy.float64. The average of the loss.

Raises:
RuntimeError: If the total number is 0.
"""
if self._total_num == 0:
raise RuntimeError("The 'Loss' can not be calculated, because the number of samples is 0, please "
"check whether has called update method before calling eval method.")
return self._sum_loss / self._total_num