From c20480c662e1b75e8ad6f385a3412657eba06baa Mon Sep 17 00:00:00 2001
From: Joachim Schoeberl <joachim.schoeberl@tuwien.ac.at>
Date: Fri, 15 Oct 2021 22:10:57 +0200
Subject: [PATCH] too fast with segment mapping

---
 libsrc/meshing/curvedelems.cpp | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/libsrc/meshing/curvedelems.cpp b/libsrc/meshing/curvedelems.cpp
index 21237782..89401625 100644
--- a/libsrc/meshing/curvedelems.cpp
+++ b/libsrc/meshing/curvedelems.cpp
@@ -1435,9 +1435,9 @@ namespace netgen
         if (seg.GetNP() == 2)
           {
             if (x)
-              *x = Point<3,T>((1-xi) * Vec<3>(mesh[seg.PNums()[0]]) + xi * Vec<3>(mesh[seg.PNums()[1]]));
+              *x = Point<3,T>(xi * Vec<3>(mesh[seg.PNums()[0]]) + (1-xi) * Vec<3>(mesh[seg.PNums()[1]]));
             if (dxdxi)
-              *dxdxi = Vec<3>(mesh[seg.PNums()[1]])-Vec<3>(mesh[seg.PNums()[0]]);
+              *dxdxi = Vec<3>(mesh[seg.PNums()[0]])-Vec<3>(mesh[seg.PNums()[1]]);
           }
         else
           {
@@ -1448,8 +1448,10 @@ namespace netgen
                                 + 2*xi*(xi-0.5) * Vec<3>(mesh[seg.PNums()[0]]));
               }
             if (dxdxi)
-              *dxdxi = T(1.0) * (Vec<3>(mesh[seg.PNums()[1]])-Vec<3>(mesh[seg.PNums()[0]]))
+              *dxdxi = (4*xi-1)*Vec<3>(mesh[seg.PNums()[0]])
+                + (4*xi-3)*Vec<3>(mesh[seg.PNums()[1]])
                 + (4-8*xi)*Vec<3>(mesh[seg.PNums()[2]]);
+
           }
         return;
       }