@staticmethod
def forward(ctx, input, axis=None):
    ctx.save_for_backward(input, axis)
    return (np.array([input.sum()]) if (axis is None) else input.sum(axis=axis))
@staticmethod
def forward(ctx, input, axis=None):
    ctx.save_for_backward(input, axis)
    return (np.array([input.sum()]) if (axis is None) else input.sum(axis=axis))