class torch.nn.BatchNorm2d(num_features, eps=1e-05, momentum=0.1, affine=True, track_running_stats=True)
[source]
Applies Batch Normalization over a 4D input (a mini-batch of 2D inputs with additional channel dimension) as described in the paper Batch Normalization: Accelerating Deep Network Training by Reducing Internal Covariate Shift .
The mean and standard-deviation are calculated per-dimension over the mini-batches and $\gamma$ and $\beta$ are learnable parameter vectors of size C
(where C
is the input size). By default, the elements of $\gamma$ are set to 1 and the elements of $\beta$ are set to 0. The standard-deviation is calculated via the biased estimator, equivalent to torch.var(input, unbiased=False)
.
Also by default, during training this layer keeps running estimates of its computed mean and variance, which are then used for normalization during evaluation. The running estimates are kept with a default momentum
of 0.1.
If track_running_stats
is set to False
, this layer then does not keep running estimates, and batch statistics are instead used during evaluation time as well.
Note
This momentum
argument is different from one used in optimizer classes and the conventional notion of momentum. Mathematically, the update rule for running statistics here is $\hat{x}_\text{new} = (1 - \text{momentum}) \times \hat{x} + \text{momentum} \times x_t$ , where $\hat{x}$ is the estimated statistic and $x_t$ is the new observed value.
Because the Batch Normalization is done over the C
dimension, computing statistics on (N, H, W)
slices, it’s common terminology to call this Spatial Batch Normalization.
None
for cumulative moving average (i.e. simple average). Default: 0.1True
, this module has learnable affine parameters. Default: True
True
, this module tracks the running mean and variance, and when set to False
, this module does not track such statistics, and initializes statistics buffers running_mean
and running_var
as None
. When these buffers are None
, this module always uses batch statistics. in both training and eval modes. Default: True
Examples:
>>> # With Learnable Parameters >>> m = nn.BatchNorm2d(100) >>> # Without Learnable Parameters >>> m = nn.BatchNorm2d(100, affine=False) >>> input = torch.randn(20, 100, 35, 45) >>> output = m(input)
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Licensed under the 3-clause BSD License.
https://pytorch.org/docs/1.7.0/generated/torch.nn.BatchNorm2d.html