Updates the given parameter using the corresponding gradient and state.
        Mixed precision version.

        Parameters
        ----------
        index : int
            The unique index of the parameter into the individual learning
            rates and weight decays. Learning rates and weight decay
            may be set via `set_lr_mult()` and `set_wd_mult()`, respectively.
        weight : NDArray
            The parameter to be updated.
        grad : NDArray
            The gradient of the objective with respect to this parameter.
        state : any obj
            The state returned by `create_state()`.

def update_multi_precision(self, index, weight, grad, state):
        """Updates the given parameter using the corresponding gradient and state.
        Mixed precision version.

        Parameters
        ----------
        index : int
            The unique index of the parameter into the individual learning
            rates and weight decays. Learning rates and weight decay
            may be set via `set_lr_mult()` and `set_wd_mult()`, respectively.
        weight : NDArray
            The parameter to be updated.
        grad : NDArray
            The gradient of the objective with respect to this parameter.
        state : any obj
            The state returned by `create_state()`.
        """
        if self.multi_precision and weight.dtype == numpy.float16:
            # Wrapper for mixed precision
            weight_master_copy = state[0]
            original_state = state[1]
            grad32 = grad.astype(numpy.float32)
            self.update(index, weight_master_copy, grad32, original_state)
            cast(weight_master_copy, dtype=weight.dtype, out=weight)
        else:
            self.update(index, weight, grad, state)