From 93d5cc90890c8acd4f56e0157af597ab471634d3 Mon Sep 17 00:00:00 2001
From: Wolfgang Bangerth <bangerth@math.tamu.edu>
Date: Mon, 25 Apr 2011 00:23:11 +0000
Subject: [PATCH] Only treat velocity, not pressure components.

git-svn-id: https://svn.dealii.org/trunk@23647 0785d39b-7218-0410-832d-ea1e28bc413d
---
 deal.II/examples/step-46/doc/intro.dox | 7 +++++--
 deal.II/examples/step-46/step-46.cc    | 3 ++-
 2 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/deal.II/examples/step-46/doc/intro.dox b/deal.II/examples/step-46/doc/intro.dox
index 2d146c1e1c..1a160ab388 100644
--- a/deal.II/examples/step-46/doc/intro.dox
+++ b/deal.II/examples/step-46/doc/intro.dox
@@ -384,7 +384,8 @@ solid cell is refined, yielding the following code:
 		{
 		  cell->face(f)->get_dof_indices (local_face_dof_indices, 0);
 		  for (unsigned int i=0; i<local_face_dof_indices.size(); ++i)
-		    constraints.add_line (local_face_dof_indices[i]);
+		    if (stokes_fe.face_system_to_component_index(i).first < dim)
+ 		      constraints.add_line (local_face_dof_indices[i]);
 		}
 	    }
 @endcode
@@ -397,7 +398,9 @@ $c_{tl}$ to nonzero values (using ConstraintMatrix::add_entry) or set
 $b_t$ to something nonzero (using
 ConstraintMatrix::set_inhomogeneity); doing nothing as above, funny as
 it looks, simply leaves the constraint to be $x_t=0$, which is exactly
-what we need in the current context.
+what we need in the current context. The call to
+FiniteElement::face_system_to_component_index makes sure that we only set
+boundary values to zero for velocity but not pressure components.
 
 Note that there are cases where this may yield incorrect results:
 notably, once we find a solid neighbor child to a current fluid cell,
diff --git a/deal.II/examples/step-46/step-46.cc b/deal.II/examples/step-46/step-46.cc
index 00b3101bd6..bea373cf3a 100644
--- a/deal.II/examples/step-46/step-46.cc
+++ b/deal.II/examples/step-46/step-46.cc
@@ -481,7 +481,8 @@ FluidStructureProblem<dim>::setup_dofs ()
 		{
 		  cell->face(f)->get_dof_indices (local_face_dof_indices, 0);
 		  for (unsigned int i=0; i<local_face_dof_indices.size(); ++i)
-		    constraints.add_line (local_face_dof_indices[i]);
+		    if (stokes_fe.face_system_to_component_index(i).first < dim)
+		      constraints.add_line (local_face_dof_indices[i]);
 		}
 	    }
   }
-- 
2.39.5