[examples] Add convenience functions for creating a Dune::FastAMG preconditioner

examples/stokes-taylorhood.cc

@@ -67,25 +67,6 @@ using namespace Dune;
 
 
 #if DUNE_VERSION_GT(DUNE_ISTL, 2, 10)
-template<class V, class M>
-auto makeAMGPreconditioner(const V& x, const M& m)
-{
-  using Operator = Dune::MatrixAdapter<M,V,V>;
-  using Criterion = Dune::Amg::SymmetricCriterion<M, Dune::Amg::RowSum>;
-  using AMG = Dune::Amg::FastAMG<Operator, V>;
-
-  auto parameters = Dune::Amg::Parameters();
-  parameters.setDebugLevel(0);
-  parameters.setNoPreSmoothSteps(1);
-  parameters.setNoPostSmoothSteps(1);
-
-  auto criterion = Criterion();
-  criterion.setDebugLevel(0);
-
-  auto opPtr = std::make_shared<Operator>(m);
-  return AMG(opPtr, criterion, parameters);
-}
-
 
 template<class V, class... P>
 class BlockDiagonalPreconditioner : public Preconditioner<V,V> {
@@ -355,8 +336,8 @@ int main (int argc, char *argv[]) try
   using namespace Dune::Indices;
 
   auto preconditioner = BlockDiagonalPreconditioner(x,
-                          makeAMGPreconditioner(x[_0], stiffnessMatrix[_0][_0]),
-                          makeAMGPreconditioner(x[_1], pressureMassMatrix));
+                          makeAMGPreconditioner(stiffnessMatrix[_0][_0], x[_0]),
+                          makeAMGPreconditioner(pressureMassMatrix, x[_1]));
 
   // Construct the actual iterative solver
   MINRESSolver<Vector> solver(

examples/utilities.hh

@@ -10,6 +10,10 @@
 #include <dune/common/typetraits.hh>
 #include <dune/common/concept.hh>
 
+#if DUNE_VERSION_GT(DUNE_ISTL, 2, 10)
+#include <dune/istl/paamg/fastamg.hh>
+#endif
+
 #include <dune/grid/common/rangegenerators.hh>
 
 #include <dune/functions/backends/concepts.hh>
@@ -141,6 +145,51 @@ void incorporateEssentialConstraints(const Basis& basis, Matrix& matrix, Vector&
 
 
 
+/**
+ * \brief Create a FastAMG preconditioner
+ * \tparam Matrix Type of the matrix the preconditioner should act on.
+ * \tparam Vector Type of vectors the preconditioner should act on.
+ * \param matrix The matrix used in the preconditioner
+ *
+ * This constructs a Dune::FastAMG preconditioner. With some
+ * standard arguments that are not defaulted in dune-istl.
+ */
+template<class Vector, class Matrix>
+auto makeAMGPreconditioner(const Matrix& matrix)
+{
+  using Operator = Dune::MatrixAdapter<Matrix,Vector,Vector>;
+  using Criterion = Dune::Amg::SymmetricCriterion<Matrix, Dune::Amg::RowSum>;
+  using AMG = Dune::Amg::FastAMG<Operator, Vector>;
+
+  auto parameters = Dune::Amg::Parameters();
+  parameters.setDebugLevel(0);
+  parameters.setNoPreSmoothSteps(1);
+  parameters.setNoPostSmoothSteps(1);
+
+  auto criterion = Criterion();
+  criterion.setDebugLevel(0);
+
+  auto opPtr = std::make_shared<Operator>(matrix);
+  return AMG(opPtr, criterion, parameters);
+}
+
+/**
+ * \brief Create a FastAMG preconditioner
+ * \tparam Matrix Type of the matrix the preconditioner should act on.
+ * \tparam Vector Type of vectors the preconditioner should act on.
+ * \param matrix The matrix used in the preconditioner
+ * \param dummy A dummy vector argument to enable type deduction for the Vector type.
+ *
+ * This constructs a Dune::FastAMG preconditioner.
+ */
+template<class Vector, class Matrix>
+auto makeAMGPreconditioner(const Matrix& matrix, const Vector& dummy)
+{
+  return makeAMGPreconditioner<Vector>(matrix);
+}
+
+
+
 // Compute the (i,j)-th cofactor of F
 template<class K, int d>
 constexpr K cofactor(const Dune::FieldMatrix<K,d,d>& F, std::size_t i, std::size_t j)