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d@0: Readers from the Fortran world are used to arrays stored in d@0: column-major order (sometimes called “Fortran order”). This is d@0: essentially the exact opposite of row-major order in that, here, the d@0: first dimension's index varies most quickly. d@0: d@0:
If you have an array stored in column-major order and wish to
d@0: transform it using FFTW, it is quite easy to do. When creating the
d@0: plan, simply pass the dimensions of the array to the planner in
d@0: reverse order. For example, if your array is a rank three
d@0: N x M x L matrix in column-major order, you should pass the
d@0: dimensions of the array as if it were an L x M x N matrix
d@0: (which it is, from the perspective of FFTW). This is done for you
d@0: automatically by the FFTW Fortran interface
d@0: (see Calling FFTW from Fortran).
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