Padding/Boundary conditions

[abadams]

We need some way to express padding of input tensors. The current thought is a primitive pad(expr, expr), which returns the first argument if it does no out-of-bounds reads, and otherwise returns the second argument.

[prigoyal]

@abadams I would like to help figure this out. I believe this will be very important especially when we want to do backwards with manual TC.

[prigoyal]

I want to work on this , it's important for convolution operations when backwards is involved especially. assigning to myself