Thanks @Pomo for helping me out.
The NN expects a 1x784 tensor.
I made sure of that by passing different size and got the following:
RuntimeError: size mismatch, m1: [28 x 28], m2: [784 x 30] at /pytorch/aten/src/TH/generic/THTensorMath.cpp:41
(m1 representing the tensor I’m passing)
So passing learn.predict(t_3[0].view(1,28*28)) should be ok in terms of tensor size.
The data that was used for training was a DataLoaders. comprised of train and test zip of X= 6000x748 and y=6000x1 (binary) Dataloader.
I’m certain that up to the predict function the code is correct because I copied it from the 4th lesson
https://github.com/fastai/fastbook/blob/master/clean/04_mnist_basics.ipynb