/* */
#include<stdio.h>
#include<math.h>

#define N 3  /*  */
main()
{
   int i, j, k, p;
   double a[N][N] = {{4,2,6},{1,1,2},{11,7,1}},
          b[N] = {32,10,77}, w[N];
   double pmax, s;

/* */

   for(k = 0; k < N-1; k++){
      p = k;
      pmax = fabs( a[k][k] );
      for(i = k+1; i < N; i++){
         if(fabs( a[i][k] ) > pmax){
            p = i;
            pmax = fabs( a[i][k] );
         }
      }

 /* */
      if(fabs( pmax ) < 1.0e-12){
         printf("too small pivot! \n");
         return(0);
      }
      if(p != k){
         for(i = k; i < N; i++){
            /* */
            s = a[k][i];
            a[k][i] = a[p][i];
            a[p][i] = s;
         }
         /* */
         s = b[k];
         b[k] = b[p];
         b[p] = s;
      }
/* */
      for(i = k +1; i < N; i++){
         w[i] = a[i][k] / a[k][k];
         a[i][k] = 0.0;
         /* */
         for(j = k + 1; j < N; j++){
            a[i][j] = a[i][j] - a[k][j] * w[i];
         }
         b[i] = b[i] - b[k] * w[i];
      }
   }
/* */
      for(i = N - 1; i >= 0; i--){
         for(j = i + 1; j < N; j++){
            b[i] = b[i] - a[i][j] * b[j];
            a[i][j] = 0.0;
         }
         b[i] = b[i] / a[i][i];
         a[i][i] = 1.0;
      }
/* */
      for(i = 0; i < N; i++){
         printf("x[%2d] = %12.8lf\n",i+1,b[i]);
      }
      return(0);
}