| from torch.autograd import Variable |
| import torch |
| from .module import Module |
| from .container import Sequential |
| from .activation import LogSoftmax |
| from .. import functional as F |
| |
| |
| def _assert_no_grad(variable): |
| assert not variable.requires_grad, \ |
| "nn criterions don't compute the gradient w.r.t. targets - please " \ |
| "mark these variables as volatile or not requiring gradients" |
| |
| |
| class _Loss(Module): |
| |
| def __init__(self, size_average=True): |
| super(_Loss, self).__init__() |
| self.size_average = size_average |
| |
| def forward(self, input, target): |
| _assert_no_grad(target) |
| backend_fn = getattr(self._backend, type(self).__name__) |
| return backend_fn(self.size_average)(input, target) |
| |
| |
| class _WeightedLoss(_Loss): |
| |
| def __init__(self, weight=None, size_average=True): |
| super(_WeightedLoss, self).__init__(size_average) |
| self.register_buffer('weight', weight) |
| |
| def forward(self, input, target): |
| _assert_no_grad(target) |
| backend_fn = getattr(self._backend, type(self).__name__) |
| return backend_fn(self.size_average, weight=self.weight)(input, target) |
| |
| |
| class L1Loss(_Loss): |
| r"""Creates a criterion that measures the mean absolute value of the |
| element-wise difference between input `x` and target `y`: |
| |
| :math:`{loss}(x, y) = 1/n \sum |x_i - y_i|` |
| |
| `x` and `y` arbitrary shapes with a total of `n` elements each. |
| |
| The sum operation still operates over all the elements, and divides by `n`. |
| |
| The division by `n` can be avoided if one sets the constructor argument `size_average=False` |
| """ |
| pass |
| |
| |
| class NLLLoss(_WeightedLoss): |
| r"""The negative log likelihood loss. It is useful to train a classification problem with n classes |
| |
| If provided, the optional argument `weights` should be a 1D Tensor assigning |
| weight to each of the classes. |
| |
| This is particularly useful when you have an unbalanced training set. |
| |
| The input given through a forward call is expected to contain log-probabilities |
| of each class: input has to be a 2D Tensor of size `(minibatch, n)` |
| |
| Obtaining log-probabilities in a neural network is easily achieved by |
| adding a `LogSoftmax` layer in the last layer of your network. |
| |
| You may use `CrossEntropyLoss` instead, if you prefer not to add an extra layer. |
| |
| The target that this loss expects is a class index `(0 to N-1, where N = number of classes)` |
| |
| The loss can be described as:: |
| |
| loss(x, class) = -x[class] |
| |
| or in the case of the weights argument it is specified as follows:: |
| |
| loss(x, class) = -weights[class] * x[class] |
| |
| Args: |
| weight (Tensor, optional): a manual rescaling weight given to each class. |
| If given, has to be a Tensor of size "nclasses" |
| size_average (bool, optional): By default, the losses are averaged over observations for each minibatch. |
| However, if the field size_average is set to False, |
| the losses are instead summed for each minibatch. |
| |
| |
| Shape: |
| - Input: :math:`(N, C)` where `C = number of classes` |
| - Target: :math:`(N)` where each value is `0 <= targets[i] <= C-1` |
| |
| Attributes: |
| weight: the class-weights given as input to the constructor |
| |
| Examples:: |
| |
| >>> m = nn.LogSoftmax() |
| >>> loss = nn.NLLLoss() |
| >>> # input is of size nBatch x nClasses = 3 x 5 |
| >>> input = autograd.Variable(torch.randn(3, 5), requires_grad=True) |
| >>> # each element in target has to have 0 <= value < nclasses |
| >>> target = autograd.Variable(torch.LongTensor([1, 0, 4])) |
| >>> output = loss(m(input), target) |
| >>> output.backward() |
| """ |
| pass |
| |
| |
| class NLLLoss2d(_WeightedLoss): |
| r"""This is negative log likehood loss, but for image inputs. It computes NLL loss per-pixel. |
| |
| Args: |
| weight (Tensor, optional): a manual rescaling weight given to each class. |
| If given, has to be a 1D Tensor having as many elements, as there are classes. |
| size_average: By default, the losses are averaged over observations for each minibatch. |
| However, if the field size_average is set to False, the losses |
| are instead summed for each minibatch. Default: True |
| |
| Shape: |
| - Input: :math:`(N, C, H, W)` where `C = number of classes` |
| - Target: :math:`(N, H, W)` where each value is `0 <= targets[i] <= C-1` |
| |
| Examples: |
| >>> m = nn.Conv2d(16, 32, (3, 3)).float() |
| >>> loss = nn.NLLLoss2d() |
| >>> # input is of size nBatch x nClasses x height x width |
| >>> input = autograd.Variable(torch.randn(3, 16, 10, 10)) |
| >>> # each element in target has to have 0 <= value < nclasses |
| >>> target = autograd.Variable(torch.LongTensor(3, 8, 8).random_(0, 4)) |
| >>> output = loss(m(input), target) |
| >>> output.backward() |
| """ |
| pass |
| |
| |
| class KLDivLoss(_WeightedLoss): |
| r"""The `Kullback-Leibler divergence`_ Loss |
| |
| KL divergence is a useful distance measure for continuous distributions |
| and is often useful when performing direct regression over the space of |
| (discretely sampled) continuous output distributions. |
| |
| As with `NLLLoss`, the `input` given is expected to contain |
| *log-probabilities*, however unlike `ClassNLLLoss`, `input` is not |
| restricted to a 2D Tensor, because the criterion is applied element-wise. |
| |
| This criterion expects a `target` `Tensor` of the same size as the |
| `input` `Tensor`. |
| |
| The loss can be described as: |
| |
| .. math:: loss(x, target) = 1/n \sum(target_i * (log(target_i) - x_i)) |
| |
| By default, the losses are averaged for each minibatch over observations |
| **as well as** over dimensions. However, if the field |
| `size_average` is set to `False`, the losses are instead summed. |
| |
| .. _Kullback-Leibler divergence: |
| https://en.wikipedia.org/wiki/Kullback-Leibler_divergence |
| """ |
| pass |
| |
| |
| class MSELoss(_Loss): |
| r"""Creates a criterion that measures the mean squared error between |
| `n` elements in the input `x` and target `y`: |
| |
| :math:`{loss}(x, y) = 1/n \sum |x_i - y_i|^2` |
| |
| `x` and `y` arbitrary shapes with a total of `n` elements each. |
| |
| The sum operation still operates over all the elements, and divides by `n`. |
| |
| The division by `n` can be avoided if one sets the internal variable |
| `size_average` to `False`. |
| |
| """ |
| pass |
| |
| |
| class BCELoss(_WeightedLoss): |
| r"""Creates a criterion that measures the Binary Cross Entropy |
| between the target and the output: |
| |
| .. math:: loss(o, t) = - 1/n \sum_i (t[i] * log(o[i]) + (1 - t[i]) * log(1 - o[i])) |
| |
| or in the case of the weights argument being specified: |
| |
| .. math:: loss(o, t) = - 1/n \sum_i weights[i] * (t[i] * log(o[i]) + (1 - t[i]) * log(1 - o[i])) |
| |
| This is used for measuring the error of a reconstruction in for example |
| an auto-encoder. Note that the targets `t[i]` should be numbers between 0 and 1. |
| |
| By default, the losses are averaged for each minibatch over observations |
| *as well as* over dimensions. However, if the field `size_average` is set |
| to `False`, the losses are instead summed. |
| |
| """ |
| pass |
| |
| |
| class HingeEmbeddingLoss(_Loss): |
| r"""Measures the loss given an input `x` which is a 2D mini-batch tensor |
| and a labels `y`, a 1D tensor containg values (`1` or `-1`). |
| This is usually used for measuring whether two inputs are similar or dissimilar, |
| e.g. using the L1 pairwise distance, and is typically used for learning |
| nonlinear embeddings or semi-supervised learning:: |
| |
| { x_i, if y_i == 1 |
| loss(x, y) = 1/n { |
| { max(0, margin - x_i), if y_i == -1 |
| |
| `x` and `y` arbitrary shapes with a total of `n` elements each |
| the sum operation still operates over all the elements, and divides by `n`. |
| |
| The division by `n` can be avoided if one sets the internal variable `size_average=False`. |
| |
| The `margin` has a default value of `1`, or can be set in the constructor. |
| """ |
| |
| def __init__(self, margin=1.0, size_average=True): |
| super(HingeEmbeddingLoss, self).__init__() |
| self.margin = margin |
| self.size_average = size_average |
| |
| def forward(self, input, target): |
| return self._backend.HingeEmbeddingLoss(self.margin, |
| self.size_average)(input, target) |
| |
| |
| class MultiLabelMarginLoss(_Loss): |
| r"""Creates a criterion that optimizes a multi-class multi-classification |
| hinge loss (margin-based loss) between input `x` (a 2D mini-batch `Tensor`) and |
| output `y` (which is a 2D `Tensor` of target class indices). |
| For each sample in the mini-batch:: |
| |
| loss(x, y) = sum_ij(max(0, 1 - (x[y[j]] - x[i]))) / x.size(0) |
| |
| where `i == 0` to `x.size(0)`, `j == 0` to `y.size(0)`, |
| `y[j] != 0`, and `i != y[j]` for all `i` and `j`. |
| |
| `y` and `x` must have the same size. |
| |
| The criterion only considers the first non zero `y[j]` targets. |
| |
| This allows for different samples to have variable amounts of target classes |
| """ |
| pass |
| |
| |
| class SmoothL1Loss(_Loss): |
| r"""Creates a criterion that uses a squared term if the absolute |
| element-wise error falls below 1 and an L1 term otherwise. |
| It is less sensitive to outliers than the `MSELoss` and in some cases |
| prevents exploding gradients (e.g. see "Fast R-CNN" paper by Ross Girshick). |
| Also known as the Huber loss:: |
| |
| { 0.5 * (x_i - y_i)^2, if |x_i - y_i| < 1 |
| loss(x, y) = 1/n \sum { |
| { |x_i - y_i| - 0.5, otherwise |
| |
| `x` and `y` arbitrary shapes with a total of `n` elements each |
| the sum operation still operates over all the elements, and divides by `n`. |
| |
| The division by `n` can be avoided if one sets the internal variable |
| `size_average` to `False` |
| """ |
| pass |
| |
| |
| class SoftMarginLoss(_Loss): |
| r"""Creates a criterion that optimizes a two-class classification |
| logistic loss between input `x` (a 2D mini-batch Tensor) and |
| target `y` (which is a tensor containing either `1` or `-1`). |
| |
| :: |
| |
| loss(x, y) = sum_i (log(1 + exp(-y[i]*x[i]))) / x.nelement() |
| |
| The normalization by the number of elements in the input can be disabled by |
| setting `self.size_average` to `False`. |
| """ |
| pass |
| |
| |
| class CrossEntropyLoss(_WeightedLoss): |
| r"""This criterion combines `LogSoftMax` and `NLLLoss` in one single class. |
| |
| It is useful when training a classification problem with `n` classes. |
| If provided, the optional argument `weights` should be a 1D `Tensor` |
| assigning weight to each of the classes. |
| This is particularly useful when you have an unbalanced training set. |
| |
| The `input` is expected to contain scores for each class. |
| |
| `input` has to be a 2D `Tensor` of size `batch x n`. |
| |
| This criterion expects a class index (0 to nClasses-1) as the |
| `target` for each value of a 1D tensor of size `n` |
| |
| The loss can be described as:: |
| |
| loss(x, class) = -log(exp(x[class]) / (\sum_j exp(x[j]))) |
| = -x[class] + log(\sum_j exp(x[j])) |
| |
| or in the case of the `weights` argument being specified:: |
| |
| loss(x, class) = weights[class] * (-x[class] + log(\sum_j exp(x[j]))) |
| |
| The losses are averaged across observations for each minibatch. |
| |
| Shape: |
| - Input: :math:`(N, C)` where `C = number of classes` |
| - Target: :math:`(N)` where each value is `0 <= targets[i] <= C-1` |
| |
| """ |
| |
| def forward(self, input, target): |
| _assert_no_grad(target) |
| return F.cross_entropy(input, target, |
| self.weight, self.size_average) |
| |
| |
| class MultiLabelSoftMarginLoss(_WeightedLoss): |
| r"""Creates a criterion that optimizes a multi-label one-versus-all |
| loss based on max-entropy, between input `x` (a 2D mini-batch `Tensor`) and |
| target `y` (a binary 2D `Tensor`). For each sample in the minibatch:: |
| |
| loss(x, y) = - sum_i (y[i] log( exp(x[i]) / (1 + exp(x[i]))) |
| + (1-y[i]) log(1/(1+exp(x[i])))) / x:nElement() |
| |
| where `i == 0` to `x.nElement()-1`, `y[i] in {0,1}`. |
| `y` and `x` must have the same size. |
| """ |
| |
| def forward(self, input, target): |
| return F.binary_cross_entropy(torch.sigmoid(input), target, |
| self.weight, self.size_average) |
| |
| |
| class CosineEmbeddingLoss(Module): |
| r"""Creates a criterion that measures the loss given an input tensors x1, x2 |
| and a `Tensor` label `y` with values 1 or -1. |
| This is used for measuring whether two inputs are similar or dissimilar, |
| using the cosine distance, and is typically used for learning nonlinear |
| embeddings or semi-supervised learning. |
| |
| `margin` should be a number from `-1` to `1`, `0` to `0.5` is suggested. |
| If `margin` is missing, the default value is `0`. |
| |
| The loss function for each sample is:: |
| |
| { 1 - cos(x1, x2), if y == 1 |
| loss(x, y) = { |
| { max(0, cos(x1, x2) - margin), if y == -1 |
| |
| If the internal variable `size_average` is equal to `True`, |
| the loss function averages the loss over the batch samples; |
| if `size_average` is `False`, then the loss function sums over the |
| batch samples. By default, `size_average = True`. |
| """ |
| |
| def __init__(self, margin=0, size_average=True): |
| super(CosineEmbeddingLoss, self).__init__() |
| self.margin = margin |
| self.size_average = size_average |
| |
| def forward(self, input1, input2, target): |
| return self._backend.CosineEmbeddingLoss(self.margin, |
| self.size_average)(input1, input2, target) |
| |
| |
| class MarginRankingLoss(Module): |
| r"""Creates a criterion that measures the loss given |
| inputs `x1`, `x2`, two 1D mini-batch `Tensor`s, |
| and a label 1D mini-batch tensor `y` with values (`1` or `-1`). |
| |
| If `y == 1` then it assumed the first input should be ranked higher |
| (have a larger value) than the second input, and vice-versa for `y == -1`. |
| |
| The loss function for each sample in the mini-batch is:: |
| |
| loss(x, y) = max(0, -y * (x1 - x2) + margin) |
| |
| if the internal variable `size_average = True`, |
| the loss function averages the loss over the batch samples; |
| if `size_average = False`, then the loss function sums over the batch samples. |
| By default, `size_average` equals to `True`. |
| """ |
| |
| def __init__(self, margin=0, size_average=True): |
| super(MarginRankingLoss, self).__init__() |
| self.margin = margin |
| self.size_average = size_average |
| |
| def forward(self, input1, input2, target): |
| return self._backend.MarginRankingLoss(self.margin, |
| self.size_average)(input1, input2, target) |
| |
| |
| class MultiMarginLoss(Module): |
| r"""Creates a criterion that optimizes a multi-class classification hinge loss |
| (margin-based loss) between input `x` (a 2D mini-batch `Tensor`) and |
| output `y` (which is a 1D tensor of target class indices, `0` <= `y` <= `x.size(1)`): |
| |
| For each mini-batch sample:: |
| |
| loss(x, y) = sum_i(max(0, (margin - x[y] + x[i]))^p) / x.size(0) |
| where `i == 0` to `x.size(0)` and `i != y`. |
| |
| Optionally, you can give non-equal weighting on the classes by passing |
| a 1D `weights` tensor into the constructor. |
| |
| The loss function then becomes: |
| |
| loss(x, y) = sum_i(max(0, w[y] * (margin - x[y] - x[i]))^p) / x.size(0) |
| |
| By default, the losses are averaged over observations for each minibatch. |
| However, if the field `size_average` is set to `False`, |
| the losses are instead summed. |
| """ |
| |
| def __init__(self, p=1, margin=1, weight=None, size_average=True): |
| super(MultiMarginLoss, self).__init__() |
| if p != 1 and p != 2: |
| raise ValueError("only p == 1 and p == 2 supported") |
| assert weight is None or weight.dim() == 1 |
| self.p = p |
| self.margin = margin |
| self.size_average = size_average |
| self.weight = weight |
| |
| def forward(self, input, target): |
| return self._backend.MultiMarginLoss(self.size_average, self.p, |
| self.margin, weight=self.weight)(input, target) |
| |
| |
| class TripletMarginLoss(Module): |
| r"""Creates a criterion that measures the triplet loss given an input tensors x1, x2, x3 |
| and a margin with a value greater than 0. |
| This is used for measuring a relative similarity between samples. A triplet is composed by |
| `a`, `p` and `n`: anchor, positive examples and negative example respectively. |
| The shape of all input variables should be :math:`(N, D)`. |
| |
| The distance swap is described in detail in the paper `Learning shallow convolutional feature descriptors with |
| triplet losses`_ by V. Balntas, E. Riba et al. |
| |
| .. math:: |
| L(a, p, n) = \frac{1}{N} \left( \sum_{i=1}^N \max \{d(a_i, p_i) - d(a_i, n_i) + {\rm margin}, 0\} \right) |
| |
| where :math: `d(x_i, y_i) = \| {\bf x}_i - {\bf y}_i \|_2^2`. |
| |
| Args: |
| anchor: anchor input tensor |
| positive: positive input tensor |
| negative: negative input tensor |
| p: the norm degree. Default: 2 |
| |
| Shape: |
| - Input: :math:`(N, D)` where `D = vector dimension` |
| - Output: :math:`(N, 1)` |
| |
| >>> triplet_loss = nn.TripletMarginLoss(margin=1.0, p=2) |
| >>> input1 = autograd.Variable(torch.randn(100, 128)) |
| >>> input2 = autograd.Variable(torch.randn(100, 128)) |
| >>> input3 = autograd.Variable(torch.randn(100, 128)) |
| >>> output = triplet_loss(input1, input2, input3) |
| >>> output.backward() |
| |
| .. _Learning shallow convolutional feature descriptors with triplet losses: |
| http://www.iis.ee.ic.ac.uk/%7Evbalnt/shallow_descr/TFeat_paper.pdf |
| """ |
| |
| def __init__(self, margin=1.0, p=2, eps=1e-6, swap=False): |
| super(TripletMarginLoss, self).__init__() |
| self.margin = margin |
| self.p = p |
| self.eps = eps |
| self.swap = swap |
| |
| def forward(self, anchor, positive, negative): |
| return F.triplet_margin_loss(anchor, positive, negative, self.margin, |
| self.p, self.eps, self.swap) |
| |
| # TODO: L1HingeEmbeddingCriterion |
| # TODO: MSECriterion weight |
| # TODO: ClassSimplexCriterion |
