gauss Class Reference

#include <gauss.h>

Static Public Member Functions
static double	gaussian (double, double, int)

Detailed Description

Definition at line 10 of file gauss.h.

Member Function Documentation

gaussian()

double gauss::gaussian ( double mean, double std, int seed )

static

This function takes as parameters real valued mean and standard-deviation, and an integer valued seed. It returns a real number which may be interpreted as a sample of a normally distributed (Gaussian) random variable with the specified mean and standard deviation. After the first call to gauss, the seed parameter is ignored.

The computational technique used is to pass a uniformly distributed random number through the inverse of the Normal Distribution function.

SPDX-FileCopyrightText: 1982-1989 Donald H. House x@unk.nosp@m.nown.nosp@m..com SPDX-FileCopyrightText: 1989 Robert Allen x@unk.nosp@m.nown.nosp@m..com SPDX-License-Identifier: GPL-2.0-or-later

Definition at line 20 of file gauss.cpp.

{
 
#define itblmax 20 /* length - 1 of table describing F inverse */
#define didu 40.0 /* delta table position / delta ind. variable */
    /* itblmax / 0.5 */
 
    /* interpolation table for F inverse */
    static double tbl[] = {0.00000E+00, 6.27500E-02, 1.25641E-01, 1.89000E-01,
                           2.53333E-01, 3.18684E-01, 3.85405E-01, 4.53889E-01,
                           5.24412E-01, 5.97647E-01, 6.74375E-01, 7.55333E-01,
                           8.41482E-01, 9.34615E-01, 1.03652E+00, 1.15048E+00,
                           1.28167E+00, 1.43933E+00, 1.64500E+00, 1.96000E+00,
                           3.87000E+00
                          };
 
    static int first_time = 1;
 
    double u;
    double di;
    int index, minus;
    double delta, gaussian_random_value;
 
    if (first_time) {
        srand48(seed);
        first_time = 0;
    }
    /*
      compute uniform random number between 0.0 - 0.5, and a sign with
      probability 1/2 of being either + or -
    */
    u = drand48();
    if (u >= 0.5) {
        minus = 0;
        u = u - 0.5;
    }
    else {
        minus = 1;
    }
    /* interpolate gaussian random number using table */
 
    index = (int)(di = (didu * u));
    if (index == itblmax) {
        delta = tbl[index];
    }
    else {
        di -= index;
        delta =  tbl[index] + (tbl[index + 1] - tbl[index]) * di;
    }
    gaussian_random_value = mean + std * (minus ? -delta : delta);
 
    return(gaussian_random_value);
}

References didu, itblmax, and u.

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The documentation for this class was generated from the following files:

• plugins/paintops/hairy/gauss.h
• plugins/paintops/hairy/gauss.cpp