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# C:/Musimathics_local/Musimat/MusimatChapter9/C091704d.cpp

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    00001 #include "MusimatChapter9.h"
    00002 MusimatChapter9Section(C091704d) {
    00003 Print("*** Voss’s Method ***");
    00004 /*****************************************************************************
    00005
    00006 Voss’s Method
    00007
    00008 Martin Gardner (1978) reported a fractal noise generator attributed to Voss. A
    00009 set of random variables xk are summed on each sample n, and the result is output. The random vari-
    00010 ables are updated at different rates. If , then the k th variable is assigned a new random
    00011 number Us. The index k ranges from 0 to N – 1. So x0 is randomized every sample, x1 is randomized
    00012 every other sample, x2 is randomized every fourth sample, and so on, until finally xN–1 is only
    00013 randomized every  samples.  We can code this method as follows:
    00014 *****************************************************************************/
    00015         para1(); // Step into this function to continue.
    00016 }
    00017
    00018 Real VossFracRand( Integer n, RealList L ) {
    00019         Real sum = 0.0;
    00020         Integer N = Length( L );
    00021         For(Integer k = 0; k < N; k = k + 1) {
    00022                 If (Mod(n, Integer(Pow(2, k))) == 0) {
    00023                          L[k] = Random(-1.0, 1.0);
    00024                 }
    00025                 sum = sum + L[ k ];
    00026         }
    00027         Return(sum);
    00028 }
    00029
    00030 Static Void para1() {
    00031 /*****************************************************************************
    00032 The following creates and prints a list of 128 fractal noise samples over four octaves:
    00033 *****************************************************************************/
    00034
    00035 RealList L(Random(), Random(), Random(), Random());
    00036 RealList R;
    00037
    00038 For (Integer n = 0; n < 128; n = n + 1) {
    00039         R[n] = VossFracRand(n, L);
    00040 }
    00041
    00042 Print("*** Voss' Fractal Method ***");
    00043 Print(R);
    00044
    00045 /*****************************************************************************
    00046 Figure 9.32 shows how this noise is constructed by this method. Each function changes at a rate
    00047 twice as fast as the previous function, and the functions are summed. Random values in the rapidly
    00048 changing functions have only local influence, whereas values in the slowly changing functions extend
    00049 their influence over many samples of the summed result, giving the result a fractal characteristic.
    00050 *****************************************************************************/
    00051 }}
    00052
    00054 /* $Revision: 1.2 $ $Date: 2006/09/09 06:22:44 $ $Author: dgl $ $Name:  $ $Id: _c091704d_8cpp-source.html,v 1.2 2006/09/09 06:22:44 dgl Exp $ */
    00055 // The Musimat Tutorial © 2006 Gareth Loy
    00056 // Derived from Chapter 9 and Appendix B of "Musimathics Vol. 1" © 2006 Gareth Loy
    00057 // and published exclusively by The MIT Press.
    00058 // This program is released WITHOUT ANY WARRANTY; without even the implied
    00059 // warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
    00060 // For information on usage and redistribution, and for a DISCLAIMER OF ALL
    00061 // WARRANTIES, see the file, "LICENSE.txt," in this distribution.
    00062 // "Musimathics" is available here:     http://mitpress.mit.edu/catalog/item/default.asp?ttype=2&tid=10916
    00063 // Gareth Loy's Musimathics website:    http://www.musimathics.com/
    00064 // The Musimat website:                 http://www.musimat.com/
    00065 // This program is released under the terms of the GNU General Public License
    00066 // available here:                      http://www.gnu.org/licenses/gpl.txt
    00067