Hi Bobak,
thanks for sharing your notebook! Being able to use some fastai tools such as the learning rate finder with custom models/data/loss function would be very helpful. However, with the current version of fastai (1.x), see https://github.com/fastai/fastai, your code doesn’t work anymore. For instance, I think ArraysIndexDataset doesn’t exist anymore. It would be really cool if you could update your code for the current version of fastai.