class_docstr: Implements Adam 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 Adam implements 2 fusions.
  
    * Fusion of the Adam 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.FusedAdam` may be used as a drop-in replacement for ``torch.optim.AdamW``,
  or ``torch.optim.Adam`` with ``adam_w_mode=False``::
  
      opt = apex.optimizers.FusedAdam(model.parameters(), lr = ....)
      ...
      opt.step()
  
  :class:`apex.optimizers.FusedAdam` may be used with or without Amp.  If you wish to use :class:`FusedAdam` with Amp,
  you may choose any ``opt_level``::
  
      opt = apex.optimizers.FusedAdam(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.
  
  
  .. warning::
      A previous version of :class:`FusedAdam` allowed a number of additional arguments to ``step``.  These additional arguments
      are now deprecated and unnecessary.
  
  Adam was been proposed in `Adam: A Method for Stochastic Optimization`_.
  
  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 square. (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`_
          (default: False) NOT SUPPORTED in FusedAdam!
      adam_w_mode (boolean, optional): Apply L2 regularization or weight decay
          True for decoupled weight decay(also known as AdamW) (default: True)
      set_grad_none (bool, optional): whether set grad to None when zero_grad()
          method is called. (default: True)
  
  .. _Adam - A Method for Stochastic Optimization:
      https://arxiv.org/abs/1412.6980
  .. _On the Convergence of Adam and Beyond:
      https://openreview.net/forum?id=ryQu7f-RZ
docstr: Performs a single optimization step.
  
  Arguments:
      closure (callable, optional): A closure that reevaluates the model
          and returns the loss.
  
  The remaining arguments are deprecated, and are only retained (for the moment) for error-checking purposes.
docstr_tok: ["Performs","a","single","optimization","step",".","Arguments",":","closure","(","callable",",","optional",")",":","A","closure","that","reevaluates","the","model","and","returns","the","loss",".","The","remaining","arguments","are","deprecated",",","and","are","only","retained","(","for","the","moment",")","for","error-checking","purposes","."]
code: def step(
      self,
      closure=None,
      grads=None,
      output_params=None,
      scale=None,
      grad_norms=None,
      grad_scaler=None,
  ):
      """Performs a single optimization step.
  
      Arguments:
          closure (callable, optional): A closure that reevaluates the model
              and returns the loss.
  
      The remaining arguments are deprecated, and are only retained (for the moment) for error-checking purposes.
      """
      if any(
          p is not None
          for p in [grads, output_params, scale, grad_norms]
      ):
          raise RuntimeError(
              "FusedAdam has been updated.  Simply initialize it identically to torch.optim.Adam, and call step() with no arguments."
          )
      loss = None
      if closure is not None:
          loss = closure()
  
      for group in self.param_groups:
          if len(group["params"]) == 0:
              continue
          bias_correction = 1 if group["bias_correction"] else 0
          beta1, beta2 = group["betas"]
  
          # assume same step across group now to simplify things
          # per parameter step can be easily support by making it tensor, or pass list into kernel
          if "step" not in group:
              group["step"] = 0
  
          # create lists for multi-tensor apply
          g_16, p_16, m_16, v_16 = [], [], [], []
          g_bf, p_bf, m_bf, v_bf = [], [], [], []
          g_32, p_32, m_32, v_32 = [], [], [], []
  
          for p in group["params"]:
              if p.grad is None:
                  continue
              if p.grad.data.is_sparse:
                  raise RuntimeError(
                      "FusedAdam does not support sparse gradients, please consider SparseAdam instead"
                  )
  
              state = self.state[p]
              # State initialization
              if len(state) == 0:
                  # DeepSpeed ZeRO 3 processes each subgroup a time, so we need to keep tracking step count for each tensor separately.
                  # While this is not an issue for ZeRO 1 & 2, since they apply a single optimization step to the whole param group at the same time.
                  # In order to keep backward compatibility for the existing checkpoints, we use group['state'] to initialize state['step'] if it exists.
                  state["step"] = group.get("step", 0)
                  # Exponential moving average of gradient values
                  state["exp_avg"] = torch.zeros_like(p.data)
                  # Exponential moving average of squared gradient values
                  state["exp_avg_sq"] = torch.zeros_like(p.data)
  
              if p.dtype == torch.float16:
                  g_16.append(p.grad.data)
                  p_16.append(p.data)
                  m_16.append(state["exp_avg"])
                  v_16.append(state["exp_avg_sq"])
              elif p.dtype == torch.bfloat16:
                  g_bf.append(p.grad)
                  p_bf.append(p)
                  m_bf.append(state["exp_avg"])
                  v_bf.append(state["exp_avg_sq"])
              elif p.dtype == torch.float32:
                  g_32.append(p.grad.data)
                  p_32.append(p.data)
                  m_32.append(state["exp_avg"])
                  v_32.append(state["exp_avg_sq"])
              else:
                  raise RuntimeError(
                      "FusedAdam only support fp16, bf16 and fp32."
                  )
  
          if len(g_16) > 0:
              state["step"] += 1
              multi_tensor_applier(
                  self.multi_tensor_adam,
                  self._dummy_overflow_buf,
                  [g_16, p_16, m_16, v_16],
                  group["lr"],
                  beta1,
                  beta2,
                  group["eps"],
                  state["step"],
                  self.adam_w_mode,
                  bias_correction,
                  group["weight_decay"],
              )
  
          if len(g_bf) > 0:
              state["step"] += 1
              multi_tensor_applier(
                  self.multi_tensor_adam,
                  self._dummy_overflow_buf,
                  [g_bf, p_bf, m_bf, v_bf],
                  group["lr"],
                  beta1,
                  beta2,
                  group["eps"],
                  state["step"],
                  self.adam_w_mode,
                  bias_correction,
                  group["weight_decay"],
              )
  
          if len(g_32) > 0:
              state["step"] += 1
              multi_tensor_applier(
                  self.multi_tensor_adam,
                  self._dummy_overflow_buf,
                  [g_32, p_32, m_32, v_32],
                  group["lr"],
                  beta1,
                  beta2,
                  group["eps"],
                  state["step"],
                  self.adam_w_mode,
                  bias_correction,
                  group["weight_decay"],
              )
  
      return loss
  
file_path: deepspeed/deepspeed/ops/adam/fused_adam.py
imports: import torch
  from .multi_tensor_apply import MultiTensorApply
  from deepspeed.accelerator import get_accelerator
  from deepspeed.ops.op_builder import FusedAdamBuilder
label_desc: Use image node_id 3 for calling the FusedAdam obj's underlying member method code with example usage: obj.step(closure, grads, output_params, scale, grad_norms, grad_scaler) and returns: loss