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## Re: [Help-gsl] QAWF integration algorithms and low frequencies

**From**: |
Brian Gough |

**Subject**: |
Re: [Help-gsl] QAWF integration algorithms and low frequencies |

**Date**: |
Wed, 17 Sep 2008 18:13:54 +0100 |

**User-agent**: |
Wanderlust/2.14.0 (Africa) Emacs/22.2 Mule/5.0 (SAKAKI) |

At Mon, 15 Sep 2008 14:15:40 +0200,
Simone Pigolotti wrote:
>* I just implemented the function *gsl_integration_qawf() *which I*
>* need to calculate some Fourier integrals. I'm testing with some*
>* simple example like the Fourier transform of a Gaussian function but*
>* it is giving me problems: the result is correct exept for very small*
>* frequencies, where the functions returns zero as a result (of course*
>* the result of the integral of the distribution X cos(omega x) for*
>* omega -> 0 should be 1). Is there any known problem with this*
>* integration scheme? Or maybe I didn't set properly the parameters?*
There are no known bugs in QAWF.
The documentation gives a brief explanation of the algorithm, it
integrates over segments of length pi/omega. This is probably the
cause of what you are seeing because the gaussian will be almost zero
over most of that range. I guess the function needs to be reasonably
slowly varying over each region.
If you think this could be handled better could you submit a bug
report with a small example program showing the problem to
address@hidden, thanks.
--
Brian Gough
GNU Scientific Library -
http://www.gnu.org/software/gsl/