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Chris@42:Readers from the Fortran world are used to arrays stored in Chris@42: column-major order (sometimes called “Fortran order”). This is Chris@42: essentially the exact opposite of row-major order in that, here, the Chris@42: first dimension’s index varies most quickly. Chris@42:
Chris@42:If you have an array stored in column-major order and wish to
Chris@42: transform it using FFTW, it is quite easy to do. When creating the
Chris@42: plan, simply pass the dimensions of the array to the planner in
Chris@42: reverse order. For example, if your array is a rank three
Chris@42: N x M x L matrix in column-major order, you should pass the
Chris@42: dimensions of the array as if it were an L x M x N matrix
Chris@42: (which it is, from the perspective of FFTW). This is done for you
Chris@42: automatically by the FFTW legacy-Fortran interface
Chris@42: (see Calling FFTW from Legacy Fortran), but you must do it
Chris@42: manually with the modern Fortran interface (see Reversing array dimensions).
Chris@42:
Chris@42: