ran1.cpp

此程序为VC++常用数值算法这本书附赠的光盘中包含了本书中全部的源代码

static double r[98];
static int iff,ix1,ix2,ix3;
double ran1(int& idum)
{
    double rm1,rm2,t;
	int m1,m2,m3,ia1,ia2,ia3,ic1,ic2,ic3,j;
	 
    m1 = 259200, ia1 = 7141, ic1 = 54773, rm1 = 0.0000038580247,
    m2 = 134456, ia2 = 8121, ic2 = 28411, rm2 = 0.0000074373773,
    m3 = 243000, ia3= 4561, ic3 = 51349;
	
    if ((idum < 0) || (iff == 0))
	{
        iff = 1;
        ix1 =  (ic1 - idum) % m1;
        ix1 = (ia1 * ix1 + ic1) % m1;
        ix2 = ix1 % m2;
        ix1 = (ia1 * ix1 + ic1) % m1;
        ix3 = ix1 % m3;
        for (j = 1; j<=97; j++)
		{
            ix1 = (ia1 * ix1 + ic1)% m1;
            ix2 = (ia2 * ix2 + ic2)% m2;
            r[j] = (double(ix1) + double(ix2) * rm2) * rm1;
        }
        idum = 1;
	}
      ix1 = (ia1 * ix1 + ic1) % m1;
      ix2 = (ia2 * ix2 + ic2) % m2;
      ix3 = (ia3 * ix3 + ic3) % m3;
      j = 1 + int((97 * ix3) / m3);
      if ((j > 97) || (j < 1)) 
	  {
		  cout<< "abnormal exit"<<endl;
	      return 1;
	  }
      t = r[j];
      r[j] = (float(ix1) + float(ix2) * rm2) * rm1;
	  return t;
}