code: def _get_optimizer(self, model_vars: VarCollection, optimizer: str):
      if optimizer == "adam":
          opt = objax.Jit(objax.optimizer.Adam(model_vars))
      elif optimizer == "lars":
          opt = objax.Jit(objax.optimizer.LARS(model_vars))
      elif optimizer == "momentum":
          opt = objax.Jit(
              objax.optimizer.Momentum(model_vars, momentum=0.9)
          )
      elif optimizer == "sgd":
          opt = objax.Jit(objax.optimizer.SGD(model_vars))
      else:
          raise ValueError
      return opt
  
imports: import math
  import unittest
  import jax.numpy
  import numpy
  import objax
  from objax.variable import TrainVar, VarCollection
label_desc: Use image node_id 2 for calling the TestOptimizers obj's underlying member method code with example usage: obj._get_optimizer(model_vars, optimizer) and returns: opt