Backward issue

[sixin-zh]

Hello,
I'd like to raise an issue regarding the function backward of class SFB1D(Function).
In the code, it checks whether there is a need to do backward depending on the needs_input_grad[0].
In my case, needs_input_grad = (False, True, False, False, False). So I still want to perform backward with resepct to the second input of the forward function. This is not done with the current implentation . Does it make sense to
replace the condition if ctx.needs_input_grad[0]: by
if ctx.needs_input_grad[0] or ctx.needs_input_grad[1]: ?

def backward(ctx, dy):
print('TO compute backward SFB1D',ctx.needs_input_grad)
dlow, dhigh = None, None
if ctx.needs_input_grad[0]:
mode = ctx.mode
g0, g1, = ctx.saved_tensors
dy = dy[:, :, None, :]

        dx = afb1d(dy, g0, g1, mode=mode, dim=3)

        dlow = dx[:, ::2, 0].contiguous()
        dhigh = dx[:, 1::2, 0].contiguous()
    return dlow, dhigh, None, None, None, None, None

best,
Sixin