no_grad
class torch.no_grad
Context-manager that disabled gradient calculation.
Disabling gradient calculation is useful for inference, when you
   are sure that you will not call "Tensor.backward()". It will reduce
   memory consumption for computations that would otherwise have
   requires_grad=True.
In this mode, the result of every computation will have
   requires_grad=False, even when the inputs have
   requires_grad=True.
This context manager is thread local; it will not affect
   computation in other threads.
Also functions as a decorator. (Make sure to instantiate with
   parenthesis.)
Note:
 No-grad is one of several mechanisms that can enable or disable
 gradients locally see Locally disabling gradient computation for
 more information on how they compare.

Note:
 This API does not apply to forward-mode AD. If you want to
 disable forward AD for a computation, you can unpack your dual
 tensors.

Example::