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From: ForthNet@willett.UUCP (ForthNet articles from GEnie)
Newsgroups: comp.lang.forth
Subject: Mathematical routines
Message-ID: <672.UUL1.3#5129@willett.UUCP>
Date: 18 Mar 90 00:23:21 GMT
Organization: Latest link in the ForthNet chain.  (Pgh, PA)
Lines: 51


 Date: 03-15-90 (22:47)              Number: 3034 (Echo)
   To: HARV                          Refer#: 3027
 From: DOUG SCHIFFER                   Read: NO
 Subj: MATHEMATICAL ROUTINES         Status: PUBLIC MESSAGE

 #define LOCAL  static
 #define BOOL   int
 #define TRUE   1
 #define FALSE  0

 double random();       /* a function which returns a uniform random
                         * number in the range [0.0 - 1.0]  */

 /****************************************************************/
        double
 randnorm()     /* Return a normally distributed random value
                   with zero mean and unit standard deviation.  */
 /*--------------------------------------------------------------*/
 {
        LOCAL BOOL first = 1;
        double d, v1, v2;

        if (first--)
        {       do
                {       v1 = 2.0 * random() - 1.0;
                        v2 = 2.0 * random() - 1.0;
                        /* v1 and v2 are each uniform on [-1, 1] */
                        d = v1 * v1 + v2 * v2;
                } while ((d <= 0.0) OR (d >= 1.0));
                /* now, the point (v1, v2) is uniform inside the unit
          * circle, excluding the origin.
                 */
                d = sqrt(-2.0 * log(d) / d);
                v1 *= d;
                v2 *= d;
                return (v1);
        }
        else
        {       first = TRUE;
                return (v2);
        }
 }

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