private int montecarlo(double[] val)
      {  int i;
         double r,sum=0;
         for(i=0;i<val.Length;i++)
            sum+=val[i];
         r = sum * rnd.NextDouble();
         sum=0;
         for(i=0;i<val.Length;i++)
         {  sum+=val[i];
            if(sum>=r) break;
         }
         return(i);
      }