From 3ec01f7d7b207a5d330a11b03c9165df4c039e77 Mon Sep 17 00:00:00 2001
From: jakobtorben <Jakob.Torben@sintef.no>
Date: Thu, 21 Nov 2024 13:18:35 +0100
Subject: [PATCH] Update second stage preconditioner for CPR instead of
 recreate

---
 opm/simulators/linalg/OwningTwoLevelPreconditioner.hpp | 8 ++------
 opm/simulators/linalg/twolevelmethodcpr.hh             | 3 ++-
 2 files changed, 4 insertions(+), 7 deletions(-)

diff --git a/opm/simulators/linalg/OwningTwoLevelPreconditioner.hpp b/opm/simulators/linalg/OwningTwoLevelPreconditioner.hpp
index 79781964a..5f32cccc6 100644
--- a/opm/simulators/linalg/OwningTwoLevelPreconditioner.hpp
+++ b/opm/simulators/linalg/OwningTwoLevelPreconditioner.hpp
@@ -183,28 +183,24 @@ private:
                                                                FlexibleSolver<CoarseOperator>,
                                                                LevelTransferPolicy>;
     using TwoLevelMethod
-        = Dune::Amg::TwoLevelMethodCpr<OperatorType, CoarseSolverPolicy, Dune::Preconditioner<VectorType, VectorType>>;
+        = Dune::Amg::TwoLevelMethodCpr<OperatorType, CoarseSolverPolicy, Dune::PreconditionerWithUpdate<VectorType, VectorType>>;
 
     // Handling parallel vs serial instantiation of preconditioner factory.
     template <class Comm>
     void updateImpl(const Comm*)
     {
         // Parallel case.
-        auto child = prm_.get_child_optional("finesmoother");
-        finesmoother_ = PrecFactory::create(linear_operator_, child ? *child : Opm::PropertyTree(), *comm_);
         twolevel_method_.updatePreconditioner(finesmoother_, coarseSolverPolicy_);
     }
 
     void updateImpl(const Dune::Amg::SequentialInformation*)
     {
         // Serial case.
-        auto child = prm_.get_child_optional("finesmoother");
-        finesmoother_ = PrecFactory::create(linear_operator_, child ? *child : Opm::PropertyTree());
         twolevel_method_.updatePreconditioner(finesmoother_, coarseSolverPolicy_);
     }
 
     const OperatorType& linear_operator_;
-    std::shared_ptr<Dune::Preconditioner<VectorType, VectorType>> finesmoother_;
+    std::shared_ptr<PreconditionerWithUpdate<VectorType, VectorType>> finesmoother_;
     const Communication* comm_;
     std::function<VectorType()> weightsCalculator_;
     VectorType weights_;
diff --git a/opm/simulators/linalg/twolevelmethodcpr.hh b/opm/simulators/linalg/twolevelmethodcpr.hh
index cb567e135..97435c82c 100644
--- a/opm/simulators/linalg/twolevelmethodcpr.hh
+++ b/opm/simulators/linalg/twolevelmethodcpr.hh
@@ -472,8 +472,9 @@ public:
   void updatePreconditioner(std::shared_ptr<SmootherType> smoother,
                             CoarseLevelSolverPolicy& coarsePolicy)
   {
-    //assume new matrix is not reallocated the new precondition should anyway be made
     smoother_ = smoother;
+    // We assume the matrix has the same sparsity structure and memory locations throughout, only the values are changed.
+    smoother_->update();
     if (coarseSolver_) {
       policy_->calculateCoarseEntries(*operator_);
       coarsePolicy.setCoarseOperator(*policy_);