MSELoss¶
- class torch.nn.MSELoss(size_average=None, reduce=None, reduction='mean')[source]¶
Creates a criterion that measures the mean squared error (squared L2 norm) between each element in the input $x$ and target $y$.
The unreduced (i.e. with
reduction
set to'none'
) loss can be described as:$\ell(x, y) = L = \{l_1,\dots,l_N\}^\top, \quad l_n = \left( x_n - y_n \right)^2,$where $N$ is the batch size. If
reduction
is not'none'
(default'mean'
), then:$\ell(x, y) = \begin{cases} \operatorname{mean}(L), & \text{if reduction} = \text{`mean';}\\ \operatorname{sum}(L), & \text{if reduction} = \text{`sum'.} \end{cases}$$x$ and $y$ are tensors of arbitrary shapes with a total of $n$ elements each.
The mean operation still operates over all the elements, and divides by $n$.
The division by $n$ can be avoided if one sets
reduction = 'sum'
.- Parameters
size_average (bool, optional) – Deprecated (see
reduction
). By default, the losses are averaged over each loss element in the batch. Note that for some losses, there are multiple elements per sample. If the fieldsize_average
is set toFalse
, the losses are instead summed for each minibatch. Ignored whenreduce
isFalse
. Default:True
reduce (bool, optional) – Deprecated (see
reduction
). By default, the losses are averaged or summed over observations for each minibatch depending onsize_average
. Whenreduce
isFalse
, returns a loss per batch element instead and ignoressize_average
. Default:True
reduction (str, optional) – Specifies the reduction to apply to the output:
'none'
|'mean'
|'sum'
.'none'
: no reduction will be applied,'mean'
: the sum of the output will be divided by the number of elements in the output,'sum'
: the output will be summed. Note:size_average
andreduce
are in the process of being deprecated, and in the meantime, specifying either of those two args will overridereduction
. Default:'mean'
- Shape:
Input: $(*)$, where $*$ means any number of dimensions.
Target: $(*)$, same shape as the input.
Examples:
>>> loss = nn.MSELoss() >>> input = torch.randn(3, 5, requires_grad=True) >>> target = torch.randn(3, 5) >>> output = loss(input, target) >>> output.backward()