message: Fix math string.
diff: @@ -135,10 +135,10 @@ protected:
  /// Limit for the number of iterations the solver is allowed to do
  int max_iter;
  - /// Convergence criterion: $ ||r||_X <= rel_{tol}*||r_0||_X $
  + /// Convergence criterion: \f$ ||r||_X <= rel_{tol}*||r_0||_X \f$
  double rel_tol;
  - /// Convergence criterion: $ ||r||_X <= abs_{tol} $
  + /// Convergence criterion: \f$ ||r||_X <= abs_{tol} \f$
  double abs_tol;
  ///@}
  