thank you. i tried with:
FL = torch.fft(f, 2) / torch.sqrt(M * N)      # (f is a torch.FloatTensor[1, 3, 400, 300])
but came across the error:
Expected an input tensor with a last dimension of size 2 representing real + imaginary components, but got input torch.FloatTensor[1, 3, 400, 300]