L1Loss#
- class brainpy.losses.L1Loss(reduction='mean')[source]#
Creates a criterion that measures the mean absolute error (MAE) between each element in the input \(x\) and target \(y\).
The unreduced (i.e. with
reduction
set to'none'
) loss can be described as:\[\ell(x, y) = L = \{l_1,\dots,l_N\}^\top, \quad l_n = \left| x_n - y_n \right|,\]where \(N\) is the batch size. If
reduction
is not'none'
(default'mean'
), then:\[\begin{split}\ell(x, y) = \begin{cases} \operatorname{mean}(L), & \text{if reduction} = \text{`mean';}\\ \operatorname{sum}(L), & \text{if reduction} = \text{`sum'.} \end{cases}\end{split}\]\(x\) and \(y\) are tensors of 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
reduction = 'sum'
.Supports real-valued and complex-valued inputs.
- Parameters:
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.
Output: scalar. If
reduction
is'none'
, then \((*)\), same shape as the input.
Examples:
>>> loss = nn.L1Loss() >>> input = bm.random.randn(3, 5) >>> target = bm.random.randn(3, 5) >>> output = loss(input, target) >>> output.backward()