in diffq/diffq.py [0:0]
def check_unused(self):
for qparam in self._qparams:
if qparam.other is not None:
continue
grad = qparam.param.grad
if grad is None or (grad == 0).all():
if qparam.logit.grad is not None:
qparam.logit.grad.data.zero_()