From: Matthias Maier <tamiko@43-1.org>
Date: Tue, 20 Mar 2018 21:07:03 +0000 (-0500)
Subject: VectorTools: Increase max iterations in project_matrix_free
X-Git-Tag: v9.0.0-rc1~295^2
X-Git-Url: https://gitweb.dealii.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=refs%2Fpull%2F6079%2Fhead;p=dealii.git

VectorTools: Increase max iterations in project_matrix_free

Here is a funny one. Running the test
  numerics/project_q_hierarchical_2
with DEAL_II_NUM_THREADS=2 OMP_NUM_THREADS=2 (as done on the tester)
worsens the reduction rate enough to run into the maximal iteration
limit. Solve this issue by slightly increasing the maximal allowed
number of iterations.
---

diff --git a/include/deal.II/numerics/vector_tools.templates.h b/include/deal.II/numerics/vector_tools.templates.h
index e4591b66e5..ca54be3b5a 100644
--- a/include/deal.II/numerics/vector_tools.templates.h
+++ b/include/deal.II/numerics/vector_tools.templates.h
@@ -1091,11 +1091,11 @@ namespace VectorTools
       }
 
       // now invert the matrix
-      // Allow for a maximum of 5*n steps to reduce the residual by 10^-12. n
+      // Allow for a maximum of 6*n steps to reduce the residual by 10^-12. n
       // steps may not be sufficient, since roundoff errors may accumulate for
       // badly conditioned matrices. This behavior can be observed, e.g. for
       // FE_Q_Hierarchical for degree higher than three.
-      ReductionControl     control(5.*rhs.size(), 0., 1e-12, false, false);
+      ReductionControl     control(6.*rhs.size(), 0., 1e-12, false, false);
       SolverCG<LinearAlgebra::distributed::Vector<Number> > cg(control);
       PreconditionJacobi<MatrixType> preconditioner;
       preconditioner.initialize(mass_matrix, 1.);