add GMRES restart option

Documentation/ProjectFile/prj/linear_solvers/linear_solver/eigen/t_restart.md

@@ -0,0 +1,7 @@
+Sets the number of iterations after which a restart of the GMRES method is performed.
+Default value is 30.
+This option is only available for the GMRES solver which is part of the unsupported Eigen modules that are available
+through OGS_USE_EIGEN_UNSUPPORTED cmake option.
+
+See following links for detail description:
+ - "Detailed Description" in https://eigen.tuxfamily.org/dox/unsupported/classEigen_1_1GMRES.html

MathLib/LinAlg/Eigen/EigenLinearSolver.cpp

@@ -92,6 +92,7 @@ class EigenIterativeLinearSolver final : public EigenLinearSolverBase
              EigenOption::getPreconName(opt.precon_type));
         _solver.setTolerance(opt.error_tolerance);
         _solver.setMaxIterations(opt.max_iterations);
+        MathLib::details::EigenIterativeLinearSolver<T_SOLVER>::setRestart(opt.restart);
 
         if (!A.isCompressed())
         {
@@ -119,8 +120,36 @@ class EigenIterativeLinearSolver final : public EigenLinearSolverBase
 
 private:
     T_SOLVER _solver;
+    void setRestart(int const /*restart*/) {
+    }
 };
 
+/// Specialization for (all) three preconditioners separately
+template <>
+void EigenIterativeLinearSolver<
+    Eigen::GMRES<EigenMatrix::RawMatrixType,
+                 Eigen::IdentityPreconditioner>>::setRestart(int const restart)
+{
+    _solver.set_restart(restart);
+    INFO("-> set restart value: {:d}", _solver.get_restart());
+}
+
+template <>
+void EigenIterativeLinearSolver<Eigen::GMRES<
+    EigenMatrix::RawMatrixType,
+    Eigen::DiagonalPreconditioner<double>>>::setRestart(int const restart)
+{
+    _solver.set_restart(restart);
+    INFO("-> set restart value: {:d}", _solver.get_restart());
+}
+
+template <>
+void EigenIterativeLinearSolver<Eigen::GMRES<EigenMatrix::RawMatrixType, Eigen::IncompleteLUT<double>>>::setRestart(int const restart)
+{
+    _solver.set_restart(restart);
+    INFO("-> set restart value: {:d}", _solver.get_restart());
+}
+
 template <template <typename, typename> class Solver, typename Precon>
 std::unique_ptr<EigenLinearSolverBase> createIterativeSolver()
 {
@@ -265,6 +294,18 @@ void EigenLinearSolver::setOption(BaseLib::ConfigTree const& option)
             "scaling is not available.");
 #endif
     }
+    if (auto restart =
+            //! \ogs_file_param{prj__linear_solvers__linear_solver__eigen__restart}
+            ptSolver->getConfigParameterOptional<int>("restart")) {
+#ifdef USE_EIGEN_UNSUPPORTED
+        _option.restart = *restart;
+#else
+        OGS_FATAL(
+            "The code is not compiled with the Eigen unsupported modules. "
+            "GMRES/GMRES option restart is not available.");
+#endif
+    }
+
 }
 
 bool EigenLinearSolver::solve(EigenMatrix &A, EigenVector& b, EigenVector &x)

MathLib/LinAlg/Eigen/EigenLinearSolver.h

@@ -59,6 +59,7 @@ class EigenLinearSolver final
 protected:
     EigenOption _option;
     std::unique_ptr<EigenLinearSolverBase> _solver;
+    void setRestart();
 };
 
 }  // namespace MathLib

MathLib/LinAlg/Eigen/EigenOption.cpp

@@ -22,6 +22,7 @@ EigenOption::EigenOption()
     error_tolerance = 1.e-16;
 #ifdef USE_EIGEN_UNSUPPORTED
     scaling = false;
+    restart = 30;
 #endif
 }
 

MathLib/LinAlg/Eigen/EigenOption.h

@@ -47,6 +47,8 @@ struct EigenOption final
 #ifdef USE_EIGEN_UNSUPPORTED
     /// Scaling the coefficient matrix and the RHS bector
     bool scaling;
+    /// Restart value for the GMRES solver
+    int restart;
 #endif
 
     /// Constructor