PoissonNLLLoss¶

class
torch.nn.
PoissonNLLLoss
(log_input: bool = True, full: bool = False, size_average=None, eps: float = 1e08, reduce=None, reduction: str = 'mean')[source]¶ Negative log likelihood loss with Poisson distribution of target.
The loss can be described as:
$\text{target} \sim \mathrm{Poisson}(\text{input}) \text{loss}(\text{input}, \text{target}) = \text{input}  \text{target} * \log(\text{input}) + \log(\text{target!})$The last term can be omitted or approximated with Stirling formula. The approximation is used for target values more than 1. For targets less or equal to 1 zeros are added to the loss.
 Parameters
log_input (bool, optional) – if
True
the loss is computed as $\exp(\text{input})  \text{target}*\text{input}$ , ifFalse
the loss is $\text{input}  \text{target}*\log(\text{input}+\text{eps})$ .full (bool, optional) –
whether to compute full loss, i. e. to add the Stirling approximation term
$\text{target}*\log(\text{target})  \text{target} + 0.5 * \log(2\pi\text{target}).$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 when reduce isFalse
. Default:True
eps (float, optional) – Small value to avoid evaluation of $\log(0)$ when
log_input = False
. Default: 1e8reduce (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 (string, 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'
Examples:
>>> loss = nn.PoissonNLLLoss() >>> log_input = torch.randn(5, 2, requires_grad=True) >>> target = torch.randn(5, 2) >>> output = loss(log_input, target) >>> output.backward()
 Shape:
Input: $(N, *)$ where $*$ means, any number of additional dimensions
Target: $(N, *)$ , same shape as the input
Output: scalar by default. If
reduction
is'none'
, then $(N, *)$ , the same shape as the input