It's unlikely that this will affect anyone, but I've found some

incorrect behavior in the treatment of *upper-face* symmetries in
ReflectionSymmetry.

I propose the attached patch. In brief, since the loop runs over the
"source" points in descending order and the "destination" points in
ascending order, then the index offset between the two sets should
just be 2 (or 1 if one is staggering the origin), rather than twice
the ghost size as in the lower-face case.

The change affects branches that are only executed upon
reflection_upper_*, so most people won't see a difference.

[Patch from Eloisa Bentivegna]


git-svn-id: http://svn.cactuscode.org/arrangements/CactusNumerical/ReflectionSymmetry/trunk@39 082bdb00-0f4f-0410-b49e-b1835e5f2039

1 files changed, 17 insertions, 2 deletions

diff --git a/src/apply.c b/src/apply.c
index 353361f..160a691 100644
--- a/src/apply.c
+++ b/src/apply.c
@@ -514,6 +514,22 @@ BndReflectVI (cGH const * restrict const cctkGH,
             ioff[d] = 0;
             idir[d] = 1;
           }
+          /* To determine the correct expressions for ioff below,
+           * consider the definitions of iimin and iimax in the macro
+           * COPY_PRE above:
+           *
+           *    iioff = ioff + (1 - idir) * imin
+           *    iimin = iioff + idir * imin
+           *    iimax = iioff + idir * imax
+           *
+           * We need idir = -1 since the loop copying into the
+           * symmetry zones traverses the grid points in opposite
+           * directions.
+           *
+           * Using the expressions above, one chooses the desired
+           * values of iimin and iimax, and can then solve the
+           * equations above for ioff.
+           */
           if (face == 0) {
             imax[dir] = cctkGH->cctk_nghostzones[dir];
             ioff[dir] = (+ 2*cctkGH->cctk_nghostzones[dir] - 1 
@@ -521,8 +537,7 @@ BndReflectVI (cGH const * restrict const cctkGH,
             idir[dir] = -1;
           } else {
             imin[dir] = cctkGH->cctk_lsh[dir] - cctkGH->cctk_nghostzones[dir];
-            ioff[dir] = (- 2*cctkGH->cctk_nghostzones[dir] + 1
-                         - (do_stagger[2*dir+face] ? 0 : 1));
+            ioff[dir] = - 1 - (do_stagger[2*dir+face] ? 0 : 1); 
             idir[dir] = -1;
           }