None type return while trying to find gradient of model's parameters

autograd
2

Hi @bsg_ssg

None is returned when the grad attribute isn’t populated during a backward call because of requires_grad being False for those tensors (parameters in your case).

Going by your code, I would say the for loop where you set params.requires_grad = True should be placed before any loss calculation or backward propagation is done.

It’d be best if you just place the params.requires_grad = True for loop outside the outermost for loop which is -
for i, j in train_loader_clean_ewc:

Let me know if you still face any errors after doing this.

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