Thank you very much for answering my questions. Now that I froze all the layers except the last fully connected layer and after changing my optimizer from

for group in policies:
    print(('group: {} has {} params, lr_mult: {}, decay_mult: {}'.format(
        group['name'], len(group['params']), group['lr_mult'], group['decay_mult'])))

optimizer = torch.optim.SGD(policies,
                           args.lr,
                           momentum=args.momentum,
                           weight_decay=args.weight_decay)


to

optimizer = torch.optim.SGD(filter(lambda p: p.requires_grad, model.parameters()), args.lr )

I am getting this error

File “main.py”, line 307, in adjust_learning_rate
param_group[‘lr’] = lr * param_group[‘lr_mult’]
KeyError: ‘lr_mult’

Any idea how I can fix it, thank you again.