public class MathTools
{
   public static double[] GaussianElim(double[][] A, double[] b)
   {
      int n = b.length;           // # variables

      double     pivot, factor;

      int i, j, k;

      /* -----------------------------
         Gaussian elimination method
         ----------------------------- */
      for (i = 0; i < n; i++)
      {  // Process row i 

         /* ---------------------
            (A) Select pivot
            --------------------- */
         pivot = A[i][i];

         /* ---------------------
            (B) Normalize row i
            --------------------- */
         for (j = 0; j < n; j++)
            A[i][j] = A[i][j]/pivot;

         b[i] = b[i]/pivot;

         /* ---------------------
            (C) Sweep using row i
            --------------------- */
         for (k = 0; k < n; k++)
         {
            if ( k != i )
            {
               factor = A[k][i];

               for (j = 0; j < n; j++)
                  A[k][j] = A[k][j] - factor*A[i][j];

               b[k] = b[k] - factor*b[i];
            }
         }
      }

      return(b);   // The answer is in double[] b
   }
}