Why do this error occur ?
>>> new.require_grad = True
>>> optimizer.add_param_group({"params": new})
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/wangshen/.local/lib/python3.5/site-packages/torch/optim/optimizer.py", line 193, in add_param_group
    raise ValueError("optimizing a parameter that doesn't require gradients")
ValueError: optimizing a parameter that doesn't require gradients