not perform any checks that rely on backward mode AD to be
        implemented. Defaults to True.
  * **fast_mode** (*bool**, **optional*) -- Fast mode for
    gradcheck and gradgradcheck is currently only implemented for
    R to R functions. If none of the inputs and outputs are
    complex a faster implementation of gradcheck that no longer
    computes the entire jacobian is run; otherwise, we fall back
    to the slow implementation.

Returns:
      True if all differences satisfy allclose condition
Return type:
      bool