From b4d4737e1617d5ddb44aa60eb866a5031e6f0898 Mon Sep 17 00:00:00 2001
From: Lukas Riedel <mail@lukasriedel.com>
Date: Tue, 31 Jul 2018 20:14:33 +0200
Subject: [PATCH] Merge branch
 '80-estimate-of-matrix-backend-entry-numbers-is-wrong' into 'master'

Resolve "Estimate of matrix backend entry numbers is wrong"

See merge request !75

Closes #80

(cherry picked from commit 31f02865cdd6bef19fd8d824139fd4f378ae2942)
---
 dune/dorie/interface/util.hh | 24 +++++++++---------------
 1 file changed, 9 insertions(+), 15 deletions(-)

diff --git a/dune/dorie/interface/util.hh b/dune/dorie/interface/util.hh
index 5bd1da6a..5eb85098 100644
--- a/dune/dorie/interface/util.hh
+++ b/dune/dorie/interface/util.hh
@@ -19,28 +19,22 @@
 namespace Dune{
 namespace Dorie{
 
-/// Return the estimation of entries per matrix row for the spatial GridOperator.
+/// Return the estimation of entries per matrix row for the spatial GridOperator
 /** This supposedly decreases matrix assembly time.
- *  The values are empirical. The actual matrix statistics can be displayed
- *  by assembling the IGO Jacobian and calling patternStatistics().
+ *  The values specify the *blocks* per row. DG assembles one block for the
+ *  actual element and one for each of its neighbors.
  *  \param dim Spatial dimension
  *  \param geo Geometry type of grid entities
- *  \return Estimated entries per matrix row
+ *  \return Estimated number of blocks per matrix row
  */
 template<typename R = std::size_t>
-R estimate_mbe_entries (const int dim, const Dune::GeometryType::BasicType geo)
+constexpr R estimate_mbe_entries (const int dim, const Dune::GeometryType::BasicType geo)
 {
-	if(geo==Dune::GeometryType::BasicType::cube){
-		if(dim==2) 		
-			return 5;
-		else if(dim==3)
-			return 7;
+	if (geo==Dune::GeometryType::BasicType::cube){
+		return 2*dim + 1;
 	}
-	else if(geo==Dune::GeometryType::BasicType::simplex){
-		if(dim==2)
-			return 13;
-		else if(dim==3) 
-			return 20;
+	else if (geo==Dune::GeometryType::BasicType::simplex){
+		return dim + 2;
 	}
 	std::cerr << "Cannot provide MBE entry estimation for given dimension and/or GeometryType!" << std::endl;
 	return 1;
-- 
2.22.0