code: def get_activation_fn(activation):
      if callable(activation):
          return activation()
      elif activation.lower() == "relu":
          return nn.ReLU()
      elif activation.lower() == "gelu":
          return nn.GELU()
      raise ValueError(
          f'{activation} is not available. You can use "relu", "gelu", or a callable'
      )
  
imports: import math
  import numpy
  from typing import Optional
  import torch
  import torch.nn
  import torch.nn.functional
  from ..common._base_windows import BaseWindows
  from ..losses.pytorch import MAE
label_desc: Use image node_id 1 for calling a global function with example usage: get_activation_fn(activation) and returns: activation, nn, nn