use ILU+ISAI as smoother for amgx

src/hyteg/ginkgo/GinkgoBlockSolver.hpp

@@ -7,8 +7,9 @@
 #include <ginkgo/core/matrix/identity.hpp>
 #include <ginkgo/core/matrix/zero.hpp>
 #include <ginkgo/core/multigrid/amgx_pgm.hpp>
+#include <ginkgo/core/preconditioner/ilu.hpp>
+#include <ginkgo/core/preconditioner/isai.hpp>
 #include <ginkgo/core/preconditioner/jacobi.hpp>
-#include <ginkgo/core/solver/bicgstab.hpp>
 #include <ginkgo/core/solver/gmres.hpp>
 #include <ginkgo/core/solver/ir.hpp>
 #include <ginkgo/core/solver/multigrid.hpp>
@@ -74,6 +75,7 @@ class GinkgoBlockSolver : public Solver< OperatorType >
  public:
    using FunctionType = typename OperatorType::srcType;
    using valueType    = typename FunctionType::valueType;
+   using indexType    = int32_t;
 
    using mtx   = gko::distributed::Matrix< valueType, int32_t >;
    using csr   = gko::matrix::Csr< valueType, int32_t >;
@@ -241,9 +243,17 @@ class GinkgoBlockSolver : public Solver< OperatorType >
             }
             else if ( velocityPreconditionerType_ == 2 )
             {
+               using lower_isai = gko::preconditioner::Isai< gko::preconditioner::isai_type::general, valueType, indexType >;
+               using upper_isai = gko::preconditioner::Isai< gko::preconditioner::isai_type::general, valueType, indexType >;
+
+               auto ilu_gen = gko::share(
+                   gko::preconditioner::Ilu< lower_isai, upper_isai >::build()
+                       //.with_factorization_factory( gko::factorization::Ilu< valueType >::build().on( solver_exec_ ) )  // doesn't make a lot of difference
+                       .on( solver_exec_ ) );
+
                auto smoother_gen =
                    gko::share( gko::solver::Ir< valueType >::build()
-                                   .with_solver( jac_gen )
+                                   .with_solver( ilu_gen )
                                    .with_relaxation_factor( 0.9 )
                                    .with_criteria( gko::stop::Iteration::build().with_max_iters( 2u ).on( solver_exec_ ) )
                                    .on( solver_exec_ ) );
@@ -257,7 +267,7 @@ class GinkgoBlockSolver : public Solver< OperatorType >
                b_pre_v = gko::share(
                    gko::solver::Multigrid::build()
                        .with_max_levels( 9u )
-                       .with_min_coarse_rows( 10u )
+                       .with_min_coarse_rows( 500u )
                        .with_pre_smoother( smoother_gen )
                        .with_post_uses_pre( true )
                        .with_mg_level( gko::share( mg_level_gen ) )
@@ -266,6 +276,19 @@ class GinkgoBlockSolver : public Solver< OperatorType >
                        .with_criteria( gko::stop::Iteration::build().with_max_iters( 1u ).on( solver_exec_ ) )
                        .on( solver_exec_ )
                        ->generate( gko::share( device_monolithic_pre->create_submatrix( block_v_span, block_v_span ) ) ) );
+
+               if(printInfo_)
+               {
+                  auto amg = gko::as< gko::solver::Multigrid >( b_pre_v );
+                  WALBERLA_LOG_INFO_ON_ROOT( "[Ginkgo AMGX] Number of levels: " << amg->get_mg_level_list().size() + 1 )
+                  for ( int i = 0; i < amg->get_mg_level_list().size(); ++i )
+                  {
+                     WALBERLA_LOG_INFO_ON_ROOT( "[Ginkgo AMGX] Level "
+                                                << amg->get_mg_level_list().size() - i << " of size "
+                                                << amg->get_mg_level_list()[i]->get_fine_op()->get_size() );
+                  }
+                  WALBERLA_LOG_INFO_ON_ROOT( "[Ginkgo AMGX] Level 0 of size " << amg->get_coarsest_solver()->get_size() );
+               }
             }
             else
             {