differentiated function.
  * **inputs** (*sequence of Tensor*) -- Inputs w.r.t. which the
    gradient will be returned (and not accumulated into ".grad").

  * **grad_outputs** (*sequence of Tensor*) -- The "vector" in the
    vector-Jacobian product. Usually gradients w.r.t. each output.
    None values can be specified for scalar Tensors or ones that
    don't require grad. If a None value would be acceptable for
    all grad_tensors, then this argument is optional. Default:
    None.

  * **retain_graph** (*bool**, **optional*) -- If "False", the
    graph used to compute the grad will be freed. Note that in
    nearly all cases setting this option to "True" is not needed
    and often can be worked around in a much more efficient way.
    Defaults to the value of "create_graph".

  * **create_graph** (*bool**, **optional*) -- If "True", graph of
    the derivative will be constructed, allowing to compute higher
