JTFS produces a non-contiguous tensor with `swap_time_frequency`

[cyrusvahidi]

In the implementation of JTFS, we introduced a new backend primitive named swap_time_frequency. This conveniently tranposes the time and frequency axes such that we can perform scattering along the frequency axis. However, Kymatio has implemented contiguity checks (for reasons that I am unaware of) that are checked when performing complex modulus and other operators.

JTFS torch currently hits a runtime error due to non-contiguous tensors that appear to be induced by swap_time_frequency before frequential scattering.

I opened PR https://github.com/kymatio/kymatio/pull/972 which simply forced the tensor returned by swap_time_frequency to be contiguous. This may be inefficient, since it clones the tensor.

This poses the following questions:

• why did we need contiguous tensors in the first place?
• can we copy the tensor and force contiguity?
• is there a more efficient approach?