From f117f429caff987314d8ce8f0fc9c1b670b97364 Mon Sep 17 00:00:00 2001
From: wolf <wolf@0785d39b-7218-0410-832d-ea1e28bc413d>
Date: Mon, 10 Sep 2001 09:05:31 +0000
Subject: [PATCH] Introduce a variable that denotes the finite difference step
 length in the computation of the second derivatives.

git-svn-id: https://svn.dealii.org/trunk@4952 0785d39b-7218-0410-832d-ea1e28bc413d
---
 deal.II/deal.II/include/fe/fe_base.h | 15 +++++++++++++++
 deal.II/deal.II/source/fe/fe.cc      | 10 ++++++----
 2 files changed, 21 insertions(+), 4 deletions(-)

diff --git a/deal.II/deal.II/include/fe/fe_base.h b/deal.II/deal.II/include/fe/fe_base.h
index f84c4f2064..f3935c6aa8 100644
--- a/deal.II/deal.II/include/fe/fe_base.h
+++ b/deal.II/deal.II/include/fe/fe_base.h
@@ -960,6 +960,21 @@ class FiniteElementBase : public Subscriptor,
 		      typename Mapping<dim>::InternalDataBase &mapping_internal,
 		      InternalDataBase                        &fe_internal,
 		      FEValuesData<dim>                       &data) const;
+
+  private:
+				     /**
+				      * Second derivatives of shapes
+				      * functions are not computed
+				      * analytically, but by finite
+				      * differences of the
+				      * gradients. This static
+				      * variable denotes the step
+				      * length to be used for
+				      * that. It's value is set to
+				      * 1e-6.
+				      */
+    static const double fd_step_length;
+    
     
 				     /**
 				      * Allow the FESystem class to
diff --git a/deal.II/deal.II/source/fe/fe.cc b/deal.II/deal.II/source/fe/fe.cc
index 8b16e29b7a..d77a428651 100644
--- a/deal.II/deal.II/source/fe/fe.cc
+++ b/deal.II/deal.II/source/fe/fe.cc
@@ -31,6 +31,10 @@ using namespace std;
 /*------------------------------- FiniteElementBase ----------------------*/
 
 
+template <int dim>
+const double FiniteElementBase<dim>::fd_step_length = 1.0e-6;
+
+
 template <int dim>
 void
 FiniteElementBase<dim>::
@@ -58,8 +62,7 @@ InternalDataBase::initialize_2nd (const FiniteElement<dim> *element,
   for (unsigned int d=0; d<dim; ++d)
     {
       Point<dim> shift;
-//TODO:[GK] unify the places where the finite differencing step length is used      
-      shift (d) = 1.e-6;
+      shift (d) = fd_step_length;
 
 				       // generate points and FEValues
 				       // objects shifted in
@@ -374,13 +377,12 @@ compute_2nd (const Mapping<dim>                   &mapping,
 	    const Tensor<1,dim>& left
 	      = fe_internal.differences[d1+dim]->shape_grad(shape, q);
 
-//TODO:[GK] unify the places where the finite differencing step length is used      
 					     // compute the second
 					     // derivative from a
 					     // symmetric difference
 					     // approximation
 	    for (unsigned int d=0; d<dim; ++d)
-	      diff_quot[d][q][d1] = 1./(2*1.e-6) * (right[d]-left[d]);
+	      diff_quot[d][q][d1] = 1./(2*fd_step_length) * (right[d]-left[d]);
 	  }
 
 				       // up to now we still have
-- 
2.39.5