For symmetric indefinite matrices it is best to use the minimum residual algorithm. The following example is slightly modified from the previous example by negating the first matrix element:

   /* minimum residual algorithm */

   /* value   row   col */
   A = { -3     1     1,
          1     2     1,
          4     2     2,
          1     3     2,
          3     4     2,
         10     3     3,
          3     4     4 };

   /* right-hand sides b = (1 1 1 1) */
   b = {1, 1, 1, 1};

   /* desired solution tolerance (optional) */
   tol = 1e-7;

   /* maximum number of iterations (optional) */
   maxit = 200;

   /* allocate iteration progress (optional) */
   hist = j(50, 1);

   /* initial guess (optional) */
   start = {2, 3, 4, 5};

   /* invoke minimum residual method */
   call itsolver (
     x, st, it,            /* output parameters */
     'minres', a, b, 'ic', /* input parameters */
     tol,                  /* optional control parameters */
     maxit,
     start,
     hist
    );

   print  x;  /* print solution */
   print st;  /* print solution tolerance */
   print it;  /* print resultant number of iterations */

                    X
                 -0.27027
                0.1891892
                0.0810811
                0.1441441

                    ST
                1.283E-15

                    IT
                        4