Adapt the solver in the Riemannian Proximal Newton solver:

Use cholmod if the dune-solvers version >= 2.8, use umfpack for older versions

dune/gfe/riemannianpnsolver.cc

@@ -11,8 +11,13 @@
 #include <dune/fufem/assemblers/localassemblers/massassembler.hh>
 #include <dune/fufem/assemblers/basisinterpolationmatrixassembler.hh>
 
-// Using a cholmod solver as the inner solver
+#if DUNE_VERSION_GTE(DUNE_SOLVERS, 2, 8)
+// Using a cholmod solver as the inner solver, available only since 2.8
 #include <dune/solvers/solvers/cholmodsolver.hh>
+#else
+// Using a umfpack solver as the inner solver
+#include <dune/solvers/solvers/umfpacksolver.hh>
+#endif
 
 #include <dune/solvers/norms/twonorm.hh>
 #include <dune/solvers/norms/h1seminorm.hh>
@@ -96,8 +101,12 @@ setup(const GridType& grid,
     //////////////////////////////////////////////////////////////////
     //   Create the inner solver using a cholmod solver
     //////////////////////////////////////////////////////////////////
-
+#if DUNE_VERSION_GTE(DUNE_SOLVERS, 2, 8)
     innerSolver_ = std::make_shared<Dune::Solvers::CholmodSolver<MatrixType,CorrectionType> >();
+#else
+    std::cout << "using umfpacksolver" << std::endl;
+    innerSolver_ = std::make_shared<Dune::Solvers::UMFPackSolver<MatrixType,CorrectionType> >();
+#endif
     innerSolver_->setIgnore(*globalDirichletNodes);
 
     // //////////////////////////////////////////////////////////////////////////////////////

dune/gfe/riemannianpnsolver.hh

@@ -13,7 +13,11 @@
 #include <dune/solvers/common/boxconstraint.hh>
 #include <dune/solvers/norms/h1seminorm.hh>
 #include <dune/solvers/solvers/iterativesolver.hh>
+#if DUNE_VERSION_GTE(DUNE_SOLVERS, 2, 8)
 #include <dune/solvers/solvers/cholmodsolver.hh>
+#else
+#include <dune/solvers/solvers/umfpacksolver.hh>
+#endif
 
 #include <dune/gfe/periodic1dpq1nodalbasis.hh>
 
@@ -67,7 +71,7 @@ public:
           hessianMatrix_(nullptr), h1SemiNorm_(NULL)
     {}
 
-    /** \brief Set up the solver using a choldmod solver as the inner solver */
+    /** \brief Set up the solver using a choldmod or umfpack solver as the inner solver */
     void setup(const GridType& grid,
                const Assembler* assembler,
                const SolutionType& x,
@@ -123,8 +127,11 @@ protected:
     const Assembler* assembler_;
 
     /** \brief The solver for the quadratic inner problems */
+#if DUNE_VERSION_GTE(DUNE_SOLVERS, 2, 8)
     std::shared_ptr<typename Dune::Solvers::CholmodSolver<MatrixType,CorrectionType>> innerSolver_;
-
+#else
+    std::shared_ptr<typename Dune::Solvers::UMFPackSolver<MatrixType,CorrectionType>> innerSolver_;
+#endif
     /** \brief The Dirichlet nodes */
     const Dune::BitSetVector<blocksize>* ignoreNodes_;
 

src/cosserat-continuum.cc

@@ -575,9 +575,6 @@ int main (int argc, char *argv[]) try
                 solver.solve();
                 xTargetSpace = solver.getSol();
             } else { //parameterSet.get<std::string>("solvertype") == "proximalNewton"
-#if DUNE_VERSION_LT(DUNE_COMMON, 2, 8)
-                DUNE_THROW(Exception, "Please install dune-solvers >= 2.8 to use the Proximal Newton Solver with Cholmod!");
-#else
                 RiemannianProximalNewtonSolver<DeformationFEBasis, TargetSpace> solver;
                 solver.setup(*grid,
                              &assembler,
@@ -590,7 +587,6 @@ int main (int argc, char *argv[]) try
                 solver.setInitialIterate(xTargetSpace);
                 solver.solve();
                 xTargetSpace = solver.getSol();
-#endif
             }
 
             for (int i = 0; i < xTargetSpace.size(); i++) {