This section describes the differences between the way NAG and FFTPACK store arrays of Fourier coefficients. In the following, the Fourier transform of an array of N data values is represented by a sequence of N complex values [A0+i*B0], [A1+i*B1], ..., [A(N-1)+i*B(N-1)].
The differences are basically in the organisation of the Fourier coefficients within the returned array, and also in the normalisation. The normalisation of the FFTPACK values is such that doing a forward transform followed by a backward transform will result in the original array values being multiplied by a factor of N.
Routines to do conversions between FFTPACK and NAG formats have been added to the library.
PDA [1ex