for (k=0;k<n-1;k++) {
    for (i=n-1; i>k; i--) {
      if (abs(matice[i][k])>abs(matice[i-1][k])) {
        for (j=0; j<n+1; j++) {
          matice[i][j]+= matice[i-1][j];
          matice[i-1][j]= matice[i][j]- matice[i-1][j];
          matice[i][j]-= matice[i-1][j];
        }
      }
    }
    for (i=k+1; i<n; i++) {
      if (matice[i][k]!=0){
        x=(double) matice[k][k]/matice[i][k];
        for (j=k; j<n+1; j++) {
          matice[i][j]*=-x;
          matice[i][j]+=matice[k][j];
        }
      }
    }
  }