WG: [PD] fft algorithms

Krzysztof Czaja czaja at chopin.edu.pl
Wed Apr 10 15:02:12 CEST 2002

hi Thomas,

it looks like your 2nd requirement is met for rfftw:

``FFTW's one-dimensional real transforms store hermitian arrays as
"halfcomplex" arrays. A halfcomplex array of size n is a
one-dimensional array of n `fftw_real' numbers. A hermitian array
X in stored into a halfcomplex array Y as follows. For all
integers i such that 0 <= i <= n / 2, we have Y[i] = Re(X[i]). For
all integers i such that 0 < i < n / 2, we have Y[n-i] =

The actual `real2hc' codelets use separate real and imag arrays.


Thomas Grill wrote:
 > following properties:
 > - in-place (or with a small workspace)
 > - separated vectors for real and imaginary data, with stride factors
 > - preferably also mixed-radix (for non-power-2 transforms)
 > Alternatively, as FFTW exists (but doesn't fulfill the 2nd requirement):
 > - is there an algorithm that transforms a vector of complex points into
 > separated real and imaginary vectors in place?

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