Add indexing to pytorch meshgrid

[rbischof]

I am receiving warnings from pytorch when using the vsi metric:
UserWarning: torch.meshgrid: in an upcoming release, it will be required to pass the indexing argument.

There is a note in the pytorch documentation for meshgrid:
torch.meshgrid(*tensors) currently has the same behavior as calling numpy.meshgrid(*arrays, indexing=’ij’).
In the future torch.meshgrid will transition to indexing=’xy’ as the default.

It is necessary to add indexing=’ij’ in the call to meshgrid here to keep the same functionality.