class_docstr: Implements LAMB algorithm.
  
  Currently GPU-only.  Requires Apex to be installed via
  ``pip install -v --no-cache-dir --global-option="--cpp_ext" --global-option="--cuda_ext" ./``.
  
  This version of fused LAMB implements 2 fusions.
  
    * Fusion of the LAMB update's elementwise operations
    * A multi-tensor apply launch that batches the elementwise updates applied to all the model's parameters into one or a few kernel launches.
  
  :class:`apex.optimizers.FusedLAMB`'s usage is identical to any ordinary Pytorch optimizer::
  
      opt = apex.optimizers.FusedLAMB(model.parameters(), lr = ....)
      ...
      opt.step()
  
  :class:`apex.optimizers.FusedLAMB` may be used with or without Amp.  If you wish to use :class:`FusedLAMB` with Amp,
  you may choose any ``opt_level``::
  
      opt = apex.optimizers.FusedLAMB(model.parameters(), lr = ....)
      model, opt = amp.initialize(model, opt, opt_level="O0" or "O1 or "O2")
      ...
      opt.step()
  
  In general, ``opt_level="O1"`` is recommended.
  
  LAMB was proposed in `Large Batch Optimization for Deep Learning: Training BERT in 76 minutes`_.
  
  Arguments:
      params (iterable): iterable of parameters to optimize or dicts defining
          parameter groups.
      lr (float, optional): learning rate. (default: 1e-3)
      betas (Tuple[float, float], optional): coefficients used for computing
          running averages of gradient and its norm. (default: (0.9, 0.999))
      eps (float, optional): term added to the denominator to improve
          numerical stability. (default: 1e-8)
      weight_decay (float, optional): weight decay (L2 penalty) (default: 0)
      amsgrad (boolean, optional): whether to use the AMSGrad variant of this
          algorithm from the paper `On the Convergence of Adam and Beyond`_
          NOT SUPPORTED now! (default: False)
      adam_w_mode (boolean, optional): Apply L2 regularization or weight decay
          True for decoupled weight decay(also known as AdamW) (default: True)
      grad_averaging (bool, optional): whether apply (1-beta2) to grad when
          calculating running averages of gradient. (default: True)
      set_grad_none (bool, optional): whether set grad to None when zero_grad()
          method is called. (default: True)
      max_grad_norm (float, optional): value used to clip global grad norm
          (default: 1.0)
      use_nvlamb (boolean, optional): Apply adaptive learning rate to 0.0
          weight decay parameter (default: False)
  
  .. _Large Batch Optimization for Deep Learning - Training BERT in 76 minutes:
      https://arxiv.org/abs/1904.00962
  .. _On the Convergence of Adam and Beyond:
      https://openreview.net/forum?id=ryQu7f-RZ
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code: def zero_grad(self):
      if self.set_grad_none:
          for group in self.param_groups:
              for p in group["params"]:
                  p.grad = None
      else:
          super(FusedLAMB, self).zero_grad()
  
imports: import torch
  from apex.multi_tensor_apply import multi_tensor_applier
label_desc: Use image node_id 2 for calling the FusedLAMB obj's underlying member method code with example usage: obj.zero_grad() without return types