Feature/proximal newton solver

Introduce a Riemannian Proximal-Newton Solver as an alternative for the Trust-Region Solver. Also add 3 cleanup commits.

dune/gfe/riemanniantrsolver.cc

@@ -403,6 +403,7 @@ void RiemannianTrustRegionSolver<Basis,TargetSpace>::solve()
                                                    *hessianMatrix_,
                                                    i==0    // assemble occupation pattern only for the first call
                                                    );
+            std::cout << "Assembly took " << gradientTimer.elapsed() << " sec." << std::endl;
 
             rhs *= -1;        // The right hand side is the _negative_ gradient
 
@@ -418,11 +419,12 @@ void RiemannianTrustRegionSolver<Basis,TargetSpace>::solve()
                 if ((*mgStep->ignoreNodes_)[j][k])  // global Dirichlet nodes set
                   gradient[j][k] = 0;
 
+            if (this->verbosity_ == Solver::FULL and rank==0) {
+              std::cout << "Gradient operator norm: " << l2Norm_->operator()(gradient) << std::endl;
+              std::cout << "Gradient norm: " << gradient.two_norm() << std::endl;
+            }
             if (this->verbosity_ == Solver::FULL and rank==0)
-              std::cout << "Gradient norm: " << l2Norm_->operator()(gradient) << std::endl;
-
-            if (this->verbosity_ == Solver::FULL)
-              std::cout << "Assembly took " << gradientTimer.elapsed() << " sec." << std::endl;
+              std::cout << "Oveall assembly took " << gradientTimer.elapsed() << " sec." << std::endl;
             totalAssemblyTime += gradientTimer.elapsed();
 
             // Transfer matrix data
@@ -467,8 +469,7 @@ void RiemannianTrustRegionSolver<Basis,TargetSpace>::solve()
 
             if (mgStep && solved)
                 corr_global = mgStep->getSol();
-
-            //std::cout << "Correction: " << std::endl << corr_global << std::endl;
+                std::cout << "Two norm of the correction: " << corr_global.two_norm() << std::endl;
         }
 
         // Distribute solution