Create a congruential random numbers

Question

I want to create a congruential random numbers generator in java:
Below is the formula for it.
ri+1=(a*ri+b) mod M .
How can I use Math class for this?

Answer 1

Your guess w.r.t. a and b being constants is right. An ordinary multiple congruence random number
generator simply looks as you described:
x[n+1]= (a*x[n]+b)%M
But there's a bit more to it: a and b have to be relatively prime, i.e. gcd(a, b) == 1 and the same counts
for both a and b w.r.t. M, i.e. gcd(a, M) == 1 and gcd(b, M) == 1. Only then the 'cycle length' of your
generator will be maximal. In practice M is a power of two (2^32 comes to mind). Here's some code:public class MGRNG {
   private int a, b, M;
   private int seed;
   // ctors
   MGRNG(int a, int b, int M) { this(a, b, M, 1); }
   MGRNG(int a, int b, int M, int seed) {
      this.a= a;
      this.b= b;
      this.M= M;
      this.seed= seed;
   // next pseudo random number
   public int next() {
      seed= (a*seed+b)%M;
      return seed;
} kind regards,
Jos