Random number generators discussion

I meant: if you only request one sample from the multinomial, and then instead of a vector, you get back the index that would have been set to 1.

class CMyDistribution : public CRandomMersenne { // use any random generator as base class
  private:
  double const * prob; double sum; int n;
  public:
  void DefineProbabilities(double const * source, int colors) {
    prob = source; n = colors; sum = 0;
    for (int i=0; i < n; i++) sum += prob[i];}

  int MakeDraw() {
    double R = sum * Random() - prob[0];
    int x = 0;
    while (R > 0. && x < n-1)  R -= prob[++x];
    return x;}
};

int main() {
  int seed = 123;
  CMyDistribution rangen;
  rangen.RandomInit(seed);

  const int ncolors = 4;
  static const double ProbabilityList[ncolors] = {3., 1., 4., 2.};
  rangen.DefineProbabilities(ProbabilityList, ncolors);
  int x = rangen.MakeDraw();

  // This will give a value in the range 0-3 with probabilities 0.3, 0.1, 0.4, 0.2 respectively
  printf("\nrandom draw = %i", x);

  return 0;
}