#include <stdlib.h> #include <math.h> double gaussrand() {     static double V1, V2, S;     static int phase = 0;     double X;     if ( phase == 0 ) {         do {             double U1 = (double)rand() / RAND_MAX;             double U2 = (double)rand() / RAND_MAX;             V1 = 2 * U1 - 1;             V2 = 2 * U2 - 1;             S = V1 * V1 + V2 * V2;         } while(S >= 1 || S == 0);         X = V1 * sqrt(-2 * log(S) / S);     } else         X = V2 * sqrt(-2 * log(S) / S);     phase = 1 - phase;     return X; }