class_docstr: synchronized batch normalization module extented from ``torch.nn.BatchNormNd``
  with the added stats reduction across multiple processes.
  :class:`apex.parallel.SyncBatchNorm` is designed to work with
  ``DistributedDataParallel``.
  
  When running in training mode, the layer reduces stats across all processes
  to increase the effective batchsize for normalization layer. This is useful
  in applications where batch size is small on a given process that would
  diminish converged accuracy of the model. The model uses collective
  communication package from ``torch.distributed``.
  
  When running in evaluation mode, the layer falls back to
  ``torch.nn.functional.batch_norm``.
  
  Args:
      num_features: :math:`C` from an expected input of size
          :math:`(N, C, L)` or :math:`L` from input of size :math:`(N, L)`
      eps: a value added to the denominator for numerical stability.
          Default: 1e-5
      momentum: the value used for the running_mean and running_var
          computation. Can be set to ``None`` for cumulative moving average
          (i.e. simple average). Default: 0.1
      affine: a boolean value that when set to ``True``, this module has
          learnable affine parameters. Default: ``True``
      track_running_stats: a boolean value that when set to ``True``, this
          module tracks the running mean and variance, and when set to ``False``,
          this module does not track such statistics and always uses batch
          statistics in both training and eval modes. Default: ``True``
  
  Example::
  
      >>> sbn = apex.parallel.SyncBatchNorm(100).cuda()
      >>> inp = torch.randn(10, 100, 14, 14).cuda()
      >>> out = sbn(inp)
      >>> inp = torch.randn(3, 100, 20).cuda()
      >>> out = sbn(inp)
code: def _specify_process_group(self, process_group):
      self.process_group = process_group
  
file_path: apex/apex/parallel/sync_batchnorm.py
imports: import torch
  from torch.nn.modules.batchnorm import _BatchNorm
  from torch.nn import functional
  from .sync_batchnorm_kernel import SyncBatchnormFunction
  from apex.parallel import ReduceOp
label_desc: Use image node_id 2 for calling the SyncBatchNorm obj's underlying member method code with example usage: obj._specify_process_group(process_group) without return types