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Article #139Re: Numerical Recipes FFT routine bugs ???
From: Dr. Steven L. Eddins
Date: Fri, 24 Jul 1992 20:37
Date: Fri, 24 Jul 1992 20:37
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croteau@ccwf.cc.utexas.edu (Ed Croteau) writes: >Does anyone have any information on the "FOUR1.C" routine in the >Numerical Recipes in C book? I believe that the routine as printed >(and on a source disk) does not properly compute the FFT (try a >simple real SIN wave and examine the imaginary). Please let me know >if I am wrong about this but it seems like the imaginary part is >frequency reversed or something similar. Perhaps your difficulty is in their definition of the DFT (Discrete Fourier Transform). See equations (12.1.7) and (12.1.9), and note that the signs in the complex exponential terms are reversed from the engineering norm. Or maybe I shouldn't say "norm"---it's reversed from the definition *I* use. ;-) -- Steve Eddins eddins@holst.eecs.uic.edu (312) 996-5771 FAX: (312) 413-0024 University of Illinois at Chicago, EECS Dept., M/C 154, 1120 SEO Bldg, Box 4348, Chicago, IL 60680
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Newsgroups: comp.dsp Path: arc1-ca.pugleaf.net!sparky!uunet!zaphod.mps.ohio-state.edu!wupost!sdd.hp.com!ux1.cso.uiuc.edu!bert.eecs.uic.edu!eddins From: eddins@bert.eecs.uic.edu (Dr. Steven L. Eddins) Subject: Re: Numerical Recipes FFT routine bugs ??? Message-ID: <1992Jul24.203717.2527@bert.eecs.uic.edu> Organization: EECS Dept., University of Illinois at Chicago References: <76535@ut-emx.uucp> Date: Fri, 24 Jul 1992 20:37:17 GMT Lines: 20