c13-4 (779567), страница 4
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The magnitudeof the smallest nonzero frequencies in the FFT is ±1/(N ∆), where N is thenumber of (complex) points in the FFT. The positive and negative frequencies towhich this filter are applied are arranged in wrap-around order.• If the measured data are real, and you want the filtered output also to be real, thenyour arbitrary filter function should obey H(−f ) = H(f )*. You can arrange thismost easily by picking an H that is real and even in f .Sample page from NUMERICAL RECIPES IN C: THE ART OF SCIENTIFIC COMPUTING (ISBN 0-521-43108-5)Copyright (C) 1988-1992 by Cambridge University Press.Programs Copyright (C) 1988-1992 by Numerical Recipes Software.Permission is granted for internet users to make one paper copy for their own personal use. Further reproduction, or any copying of machinereadable files (including this one) to any servercomputer, is strictly prohibited. To order Numerical Recipes books,diskettes, or CDROMsvisit website http://www.nr.com or call 1-800-872-7423 (North America only),or send email to trade@cup.cam.ac.uk (outside North America).}den *= m4;for (j=1;j<=m;j++) p[j] /= den;free_vector(w2,1,m);free_vector(w1,1,m4);.
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