We have explicitly found the relationship between multi-dimensional
FFT's and 1-D FFT's on a helix, linking the wavenumber vector, , in a multi-dimensional system with the wavenumber
of a helical 1-D FFT, .
Specifically, the Fourier dual of helical boundary conditions is
helical boundary conditions but with axes transposed.
We have illustrated the concepts with an example of multi-dimensional
multiple prediction.