A symmetry thorn with a 90 degree rotating symmetry. This is not yet

tested.


git-svn-id: http://svn.cactuscode.org/arrangements/CactusNumerical/RotatingSymmetry90/trunk@2 c3c03602-0f4f-0410-b3fa-d2c81c8a7dc5

8 files changed, 729 insertions, 0 deletions

diff --git a/README b/README
new file mode 100644
index 0000000..084d252
--- /dev/null
+++ b/README
@@ -0,0 +1,23 @@
+CVS info   : $Header$
+
+Cactus Code Thorn RotatingSymmetry90
+Thorn Author(s)     : Erik Schnetter <schnetter@aei.mpg.de>
+Thorn Maintainer(s) : Erik Schnetter <schnetter@aei.mpg.de>
+--------------------------------------------------------------------------
+
+Purpose of the thorn:
+
+Provide a 90 degree rotational symmetry boundary condition.  This is
+the kind of symmetry that exists e.g. in a singl black hole evolution
+when the black hole has spin.  The same setup also admits an
+additional bitant symmetry.
+
+Currently the symmetry is fixed to be located at the lower x and y
+boundaries, so that there is a rotation about the z axis.
+
+The coordinate thorn does not know about this symmetry.  You will have
+to set up the domain such that you have an upper quadrant in the x and
+y directions.
+
+This symmetry boundary condition can be mixed with arbitrary symmetry
+conditions in the z direction, e.g. bitant or periodicity.
diff --git a/doc/documentation.tex b/doc/documentation.tex
new file mode 100644
index 0000000..23b2c81
--- /dev/null
+++ b/doc/documentation.tex
@@ -0,0 +1,143 @@
+% *======================================================================*
+%  Cactus Thorn template for ThornGuide documentation
+%  Author: Ian Kelley
+%  Date: Sun Jun 02, 2002
+%  $Header$
+%
+%  Thorn documentation in the latex file doc/documentation.tex
+%  will be included in ThornGuides built with the Cactus make system.
+%  The scripts employed by the make system automatically include
+%  pages about variables, parameters and scheduling parsed from the
+%  relevant thorn CCL files.
+%
+%  This template contains guidelines which help to assure that your
+%  documentation will be correctly added to ThornGuides. More
+%  information is available in the Cactus UsersGuide.
+%
+%  Guidelines:
+%   - Do not change anything before the line
+%       % START CACTUS THORNGUIDE",
+%     except for filling in the title, author, date, etc. fields.
+%        - Each of these fields should only be on ONE line.
+%        - Author names should be separated with a \\ or a comma.
+%   - You can define your own macros, but they must appear after
+%     the START CACTUS THORNGUIDE line, and must not redefine standard
+%     latex commands.
+%   - To avoid name clashes with other thorns, 'labels', 'citations',
+%     'references', and 'image' names should conform to the following
+%     convention:
+%       ARRANGEMENT_THORN_LABEL
+%     For example, an image wave.eps in the arrangement CactusWave and
+%     thorn WaveToyC should be renamed to CactusWave_WaveToyC_wave.eps
+%   - Graphics should only be included using the graphicx package.
+%     More specifically, with the "\includegraphics" command.  Do
+%     not specify any graphic file extensions in your .tex file. This
+%     will allow us to create a PDF version of the ThornGuide
+%     via pdflatex.
+%   - References should be included with the latex "\bibitem" command.
+%   - Use \begin{abstract}...\end{abstract} instead of \abstract{...}
+%   - Do not use \appendix, instead include any appendices you need as
+%     standard sections.
+%   - For the benefit of our Perl scripts, and for future extensions,
+%     please use simple latex.
+%
+% *======================================================================*
+%
+% Example of including a graphic image:
+%    \begin{figure}[ht]
+%       \begin{center}
+%          \includegraphics[width=6cm]{MyArrangement_MyThorn_MyFigure}
+%       \end{center}
+%       \caption{Illustration of this and that}
+%       \label{MyArrangement_MyThorn_MyLabel}
+%    \end{figure}
+%
+% Example of using a label:
+%   \label{MyArrangement_MyThorn_MyLabel}
+%
+% Example of a citation:
+%    \cite{MyArrangement_MyThorn_Author99}
+%
+% Example of including a reference
+%   \bibitem{MyArrangement_MyThorn_Author99}
+%   {J. Author, {\em The Title of the Book, Journal, or periodical}, 1 (1999),
+%   1--16. {\tt http://www.nowhere.com/}}
+%
+% *======================================================================*
+
+% If you are using CVS use this line to give version information
+% $Header$
+
+\documentclass{article}
+
+% Use the Cactus ThornGuide style file
+% (Automatically used from Cactus distribution, if you have a
+%  thorn without the Cactus Flesh download this from the Cactus
+%  homepage at www.cactuscode.org)
+\usepackage{../../../../doc/latex/cactus}
+
+\begin{document}
+
+% The author of the documentation
+\author{Erik Schnetter \textless schnetter@aei.mpg.de\textgreater}
+
+% The title of the document (not necessarily the name of the Thorn)
+\title{RotatingSymmetry180}
+
+% the date your document was last changed, if your document is in CVS,
+% please use:
+\date{$ $Date$ $}
+
+\maketitle
+
+% Do not delete next line
+% START CACTUS THORNGUIDE
+
+% Add all definitions used in this documentation here
+%   \def\mydef etc
+
+% Add an abstract for this thorn's documentation
+\begin{abstract}
+
+\end{abstract}
+
+% The following sections are suggestive only.
+% Remove them or add your own.
+
+\section{Introduction}
+
+\section{Physical System}
+
+\section{Numerical Implementation}
+
+\section{Using This Thorn}
+
+\subsection{Obtaining This Thorn}
+
+\subsection{Basic Usage}
+
+\subsection{Special Behaviour}
+
+\subsection{Interaction With Other Thorns}
+
+\subsection{Examples}
+
+\subsection{Support and Feedback}
+
+\section{History}
+
+\subsection{Thorn Source Code}
+
+\subsection{Thorn Documentation}
+
+\subsection{Acknowledgements}
+
+
+\begin{thebibliography}{9}
+
+\end{thebibliography}
+
+% Do not delete next line
+% END CACTUS THORNGUIDE
+
+\end{document}
diff --git a/interface.ccl b/interface.ccl
new file mode 100644
index 0000000..46383d9
--- /dev/null
+++ b/interface.ccl
@@ -0,0 +1,33 @@
+# Interface definition for thorn RotatingSymmetry90
+# $Header$
+
+IMPLEMENTS: RotatingSymmetry90
+
+INHERITS: Slab
+
+USES INCLUDE HEADER: Slab.h
+
+
+
+CCTK_INT FUNCTION SymmetryRegister (CCTK_STRING IN sym_name)
+USES FUNCTION SymmetryRegister
+
+CCTK_INT FUNCTION                                  \
+    SymmetryRegisterGrid                           \
+         (CCTK_POINTER IN cctkGH,                  \
+          CCTK_INT IN sym_handle,                  \
+          CCTK_INT IN ARRAY which_faces,           \
+          CCTK_INT IN ARRAY symmetry_zone_width)
+USES FUNCTION SymmetryRegisterGrid
+
+
+
+CCTK_INT FUNCTION Boundary_SelectedGVs \
+  (CCTK_POINTER_TO_CONST IN  GH, \
+   CCTK_INT IN  array_size, \
+   CCTK_INT ARRAY OUT var_indicies, \
+   CCTK_INT ARRAY OUT faces, \
+   CCTK_INT ARRAY OUT boundary_widths, \
+   CCTK_INT ARRAY OUT table_handles, \
+   CCTK_STRING IN  bc_name)
+USES FUNCTION Boundary_SelectedGVs
diff --git a/param.ccl b/param.ccl
new file mode 100644
index 0000000..544d191
--- /dev/null
+++ b/param.ccl
@@ -0,0 +1,14 @@
+# Parameter definitions for thorn RotatingSymmetry90
+# $Header$
+
+BOOLEAN verbose "Produce screen output while applying boundary conditions"
+{
+} "no"
+
+BOOLEAN rotating_symmetry_90 "Apply 90 degree rotating symmetry boundary conditions?"
+{
+} "no"
+
+BOOLEAN avoid_origin "Avoid the origin?"
+{
+} "no"
diff --git a/schedule.ccl b/schedule.ccl
new file mode 100644
index 0000000..d624033
--- /dev/null
+++ b/schedule.ccl
@@ -0,0 +1,12 @@
+# Schedule definitions for thorn RotatingSymmetry90
+# $Header$
+
+SCHEDULE Rot90_RegisterSymmetry IN SymmetryRegister
+{
+  LANG: C
+} "Register symmetry boundaries"
+
+SCHEDULE Rot90_ApplyBC IN BoundaryConditions
+{
+  LANG: C
+} "Apply 90 degree rotational symmetry boundary condition"
diff --git a/src/make.code.defn b/src/make.code.defn
new file mode 100644
index 0000000..4b71cce
--- /dev/null
+++ b/src/make.code.defn
@@ -0,0 +1,8 @@
+# Main make.code.defn file for thorn RotatingSymmetry90
+# $Header$
+
+# Source files in this directory
+SRCS = rotatingsymmetry90.c registersymmetry.c
+
+# Subdirectories containing source files
+SUBDIRS = 
diff --git a/src/registersymmetry.c b/src/registersymmetry.c
new file mode 100644
index 0000000..be8999c
--- /dev/null
+++ b/src/registersymmetry.c
@@ -0,0 +1,41 @@
+/* $Header$ */
+
+#include "cctk.h"
+#include "cctk_Arguments.h"
+#include "cctk_Parameters.h"
+
+void Rot90_RegisterSymmetry (CCTK_ARGUMENTS)
+{
+  DECLARE_CCTK_ARGUMENTS;
+  DECLARE_CCTK_PARAMETERS;
+  
+  int f;
+  CCTK_INT handle;
+  CCTK_INT faces[6];
+  CCTK_INT width[6];
+  CCTK_INT ierr;
+  
+  if (rotating_symmetry_90) {
+    
+    for (f=0; f<6; ++f) {
+      faces[f] = 0;
+      width[f] = 0;
+    }
+    
+    faces[0] = 1;
+    width[0] = cctk_nghostzones[0];
+    faces[1] = 1;
+    width[1] = cctk_nghostzones[1];
+    
+    handle = SymmetryRegister ("rotating_symmetry_90");
+    if (handle < 0) {
+      CCTK_WARN (0, "Could not register symmetry boundary condition");
+    }
+    
+    ierr = SymmetryRegisterGrid (cctkGH, handle, faces, width);
+    if (ierr < 0) {
+      CCTK_WARN (0, "Could not register the symmetry boundaries -- probably some other thorn has already registered the same boundary faces for a different symmetry");
+    }
+    
+  }
+}
diff --git a/src/rotatingsymmetry90.c b/src/rotatingsymmetry90.c
new file mode 100644
index 0000000..f31bb66
--- /dev/null
+++ b/src/rotatingsymmetry90.c
@@ -0,0 +1,455 @@
+/* $Header$ */
+
+#include <assert.h>
+#include <math.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "cctk.h"
+#include "cctk_Arguments.h"
+#include "cctk_Parameters.h"
+
+#include "util_ErrorCodes.h"
+#include "util_Table.h"
+
+#include "Slab.h"
+
+
+
+int BndRot90VI (cGH const * restrict const cctkGH,
+                int const * restrict const stencil,
+                int const vi)
+{
+  DECLARE_CCTK_ARGUMENTS;
+  DECLARE_CCTK_PARAMETERS;
+  
+  int gi;
+  cGroup group;
+  cGroupDynamicData data;
+  char * restrict fullname;
+  void * restrict varptr;
+  int firstvar;
+  
+  char tensortypealias[100];
+  int numvars;
+  int index;
+  int srcvi;
+  void const * restrict srcptr;
+  int parity;
+  
+  int global_bbox[6];
+  int global_lbnd[3], global_ubnd[3];
+  int fake_bbox[6];
+  
+  CCTK_REAL x0[3], dx[3];
+  CCTK_REAL origin[3], dorigin[3];
+  int avoid_origin[3];
+  int offset[3];                /* offset 0..1 due to avoid_origin */
+  
+  struct xferinfo * restrict xferinfo;
+  
+  int have_global_bbox, have_local_bbox;
+  
+  int alldirs[2];
+  int step;
+  int ndirs;                    /* 1 for face, 2 for edge */
+  int dir[3];                   /* current face or edge */
+  int otherdir[3];              /* the other direction of the rotation */
+  int q;                        /* 0..ndirs-1 */
+  int d;                        /* 0..group.dim-1 */
+  int ierr;
+  
+  /* Check arguments */
+  assert (cctkGH);
+  assert (stencil);
+  assert (vi>=0 && vi<CCTK_NumVars());
+  
+  if (! rotating_symmetry_90) return;
+  
+  if (verbose) {
+    fullname = CCTK_FullName(vi);
+    assert (fullname);
+    CCTK_VInfo (CCTK_THORNSTRING,
+                "Applying 90 degree rotating symmetry boundary conditions to \"%s\"",
+                fullname);
+    free (fullname);
+  }
+      for (d=0; d<group.dim; ++d) {
+        x0[d] = CCTK_ORIGIN_SPACE(d);
+        dx[d] = CCTK_DELTA_SPACE(d);
+      }
+  
+  /* Get and check group info */
+  gi = CCTK_GroupIndexFromVarI (vi);
+  assert (gi>=0 && gi<CCTK_NumGroups());
+  
+  ierr = CCTK_GroupData (gi, &group);
+  assert (!ierr);
+  assert (group.grouptype == CCTK_GF);
+  assert (group.disttype == CCTK_DISTRIB_DEFAULT);
+  assert (group.stagtype == 0);
+  
+  ierr = CCTK_GroupDynamicData (cctkGH, gi, &data);
+  assert (!ierr);
+  
+  varptr = CCTK_VarDataPtrI (cctkGH, 0, vi);
+  assert (varptr);
+  
+  /* Find tensor type, source variable, and parity */
+  {
+    int table;
+    
+    numvars = CCTK_NumVarsInGroupI(gi);
+    assert (numvars>0);
+    firstvar = CCTK_FirstVarIndexI(gi);
+    assert (firstvar>=0);
+    index = vi - firstvar;
+    assert (index>=0 && index<numvars);
+    table = CCTK_GroupTagsTableI(gi);
+    assert (table>=0);
+    
+    ierr = Util_TableGetString
+      (table, sizeof tensortypealias, tensortypealias, "tensortypealias");
+    if (ierr == UTIL_ERROR_TABLE_NO_SUCH_KEY) {
+      char * groupname = CCTK_GroupName(gi);
+      assert (groupname);
+      CCTK_VWarn (1, __LINE__, __FILE__, CCTK_THORNSTRING,
+                  "Tensor type alias not declared for group \"%s\" -- assuming a scalar",
+                  groupname);
+      free (groupname);
+      strcpy (tensortypealias, "scalar");
+    } else if (ierr<0) {
+      char * groupname = CCTK_GroupName(gi);
+      assert (groupname);
+      CCTK_VWarn (0, __LINE__, __FILE__, CCTK_THORNSTRING,
+                  "Error in tensor type alias declaration for group \"%s\"",
+                  groupname);
+      free (groupname);
+    }
+    
+    if (CCTK_EQUALS (tensortypealias, "scalar")) {
+      /* scalar */
+      if (numvars != 1) {
+        char * groupname = CCTK_GroupName(gi);
+        assert (groupname);
+        CCTK_VWarn (2, __LINE__, __FILE__, CCTK_THORNSTRING,
+                    "Group \"%s\" has the tensor type alias \"scalar\", but contains more than 1 element",
+                    groupname);
+        free (groupname);
+      }
+    } else if (CCTK_EQUALS (tensortypealias, "u")) {
+      /* vector */
+      assert (numvars == 3);
+    } else if (CCTK_EQUALS (tensortypealias, "dd_sym")) {
+      /* symmetric tensor */
+      assert (numvars == 6);
+    } else {
+      char * groupname = CCTK_GroupName(gi);
+      assert (groupname);
+      CCTK_VWarn (0, __LINE__, __FILE__, CCTK_THORNSTRING,
+                  "Illegal tensor type alias for group \"%s\"",
+                  groupname);
+      free (groupname);
+    }
+  }
+  
+  {
+    int min_handle, max_handle;
+    CCTK_REAL local[6], global[6];
+    min_handle = CCTK_ReductionArrayHandle ("minimum");
+    if (min_handle<0) CCTK_WARN (0, "Could not obtain reduction handle");
+    max_handle = CCTK_ReductionArrayHandle ("maximum");
+    if (max_handle<0) CCTK_WARN (0, "Could not obtain reduction handle");
+    
+    for (d=0; d<6; ++d) local[d] = cctkGH->cctk_bbox[d];
+    ierr = CCTK_ReduceLocArrayToArray1D
+      (cctkGH, -1, max_handle, local, global, 6, CCTK_VARIABLE_REAL);
+    for (d=0; d<6; ++d) global_bbox[d] = (int)global[d];
+    
+    for (d=0; d<3; ++d) local[d] = cctkGH->cctk_lbnd[d];
+    ierr = CCTK_ReduceLocArrayToArray1D
+      (cctkGH, -1, min_handle, local, global, 3, CCTK_VARIABLE_REAL);
+    for (d=0; d<3; ++d) global_lbnd[d] = (int)global[d];
+    
+    for (d=0; d<3; ++d) local[d] = cctkGH->cctk_ubnd[d];
+    ierr = CCTK_ReduceLocArrayToArray1D
+      (cctkGH, -1, max_handle, local, global, 3, CCTK_VARIABLE_REAL);
+    for (d=0; d<3; ++d) global_ubnd[d] = (int)global[d];
+    
+    for (d=0; d<3; ++d) {
+      fake_bbox[2*d  ] = data.lbnd[d] == global_lbnd[d];
+      fake_bbox[2*d+1] = data.ubnd[d] == global_ubnd[d];
+    }
+  }
+
+  /* directions */
+  alldirs[0] = 0;
+  alldirs[1] = 1;
+  
+  /* Find grid point that corresponds to the origin */
+  for (q=0; q<2; ++q) {
+    d = alldirs[q];
+    /* x0 + dx * origin == 0 */
+    origin[d] = - x0[d] / dx[d];
+    dorigin[d] = origin[d] - floor(origin[d]);
+    if (fabs(dorigin[d]) < 1.0e-6 || fabs(dorigin[d] - 1.0) < 1.0e-6) {
+      avoid_origin[d] = 0;
+    } else if (fabs(dorigin[d] - 0.5) < 1.0e-6) {
+      avoid_origin[d] = 1;
+    } else {
+      CCTK_VWarn (0, __LINE__, __FILE__, CCTK_THORNSTRING,
+                  "The coordinate origin in the %c-direction falls neither onto a grid point nor into the middle between two grid points.",
+                  "xyz"[d]);
+    }
+    offset[d] = avoid_origin[d] ? 0 : 1;
+  }
+  
+  for (step=0; step<3; ++step) {
+    switch (step) {
+    case 0:
+      /* x face */
+      ndirs = 1;
+      dir[0] = 0;
+      otherdir[0] = 1;
+      break;
+    case 1:
+      /* y face */
+      ndirs = 1;
+      dir[0] = 1;
+      otherdir[0] = 0;
+      break;
+    case 2:
+      /* xy edge */
+      ndirs = 2;
+      dir[0] = 0;
+      dir[1] = 1;
+      otherdir[0] = 1;
+      otherdir[1] = 0;
+      break;
+    default:
+      assert (0);
+    }
+    
+    if (CCTK_EQUALS (tensortypealias, "scalar")) {
+      /* scalar */
+      srcvi = vi;
+      parity = +1;
+    } else if (CCTK_EQUALS (tensortypealias, "u")) {
+      /* vector */
+      int srcindex;
+      if      (srcindex == dir[0]) srcindex = otherdir[0], parity = +1;
+      else if (srcindex == otherdir[0]) srcindex = dir[0], parity = -1;
+      else                               srcindex = index, parity = +1;
+      srcvi = firstvar + srcindex;
+    } else if (CCTK_EQUALS (tensortypealias, "dd_sym")) {
+      /* symmetric tensor */
+      int index1, index2;
+      int srcindex1, srcindex2;
+      int srcindex;
+      switch (index) {
+      case 0: index1=0, index2=0; break;
+      case 1: index1=0, index2=1; break;
+      case 2: index1=0, index2=2; break;
+      case 3: index1=1, index2=1; break;
+      case 4: index1=1, index2=2; break;
+      case 5: index1=2, index2=2; break;
+      default: assert(0);
+      }
+      parity = +1;
+      if      (srcindex1 == dir[0]) srcindex1 = otherdir[0], parity *= +1;
+      else if (srcindex1 == otherdir[0]) srcindex1 = dir[0], parity *= -1;
+      else                               srcindex1 = index1, parity *= +1;
+      if      (srcindex2 == dir[0]) srcindex2 = otherdir[0], parity *= +1;
+      else if (srcindex2 == otherdir[0]) srcindex2 = dir[0], parity *= -1;
+      else                               srcindex2 = index2, parity *= +1;
+      {
+        int compact[3][3] = { 0,1,2, 1,3,4, 2,4,5 };
+        srcindex = compact[srcindex1][srcindex2];
+      }
+      srcvi = firstvar + srcindex;
+    } else {
+      assert (0);
+    }
+    srcptr = CCTK_VarDataPtrI (cctkGH, 0, srcvi);
+    assert (srcptr);
+    
+    have_global_bbox = 1;
+    for (q=0; q<ndirs; ++q) {
+      have_global_bbox = have_global_bbox && global_bbox[2*dir[q]];
+    }
+    if (have_global_bbox) {
+      
+      for (q=0; q<ndirs; ++q) {
+        assert (stencil[dir[q]] >= 0);
+        
+        if (data.gsh[otherdir[q]] < stencil[dir[q]] + stencil[otherdir[q]] + offset[otherdir[q]]) {
+          CCTK_VWarn (0, __LINE__, __FILE__, CCTK_THORNSTRING,
+                      "The group \"%s\" has in the %c-direction only %d grid points.  "
+                      "This is not large enough for a 90 degree rotating symmetry boundary that is %d grid points wide in the %c-direction.  "
+                      "The group needs to have at least %d grid points in the %c-direction.",
+                      CCTK_GroupNameFromVarI(vi), "xyz"[dir[q]], data.gsh[dir[q]],
+                      stencil[dir[q]],  "xyz"[otherdir[q]],
+                      stencil[dir[q]] + stencil[otherdir[q]] + offset[otherdir[q]], "xyz"[dir[q]]);
+        }
+      }
+      
+      /* Allocate slab transfer description */
+      xferinfo = malloc(group.dim * sizeof *xferinfo);
+      assert (xferinfo);
+      
+      /* Fill in slab transfer description */
+      for (d=0; d<group.dim; ++d) {
+        xferinfo[d].src.gsh         = data.gsh        [d];
+        xferinfo[d].src.lbnd        = data.lbnd       [d];
+        xferinfo[d].src.lsh         = data.lsh        [d];
+        xferinfo[d].src.lbbox       = fake_bbox       [2*d  ];
+        xferinfo[d].src.ubbox       = fake_bbox       [2*d+1];
+        xferinfo[d].src.nghostzones = data.nghostzones[d];
+        xferinfo[d].src.off         = 0;
+        xferinfo[d].src.str         = 1;
+        xferinfo[d].src.len         = data.gsh        [d];
+        
+        xferinfo[d].dst.gsh         = data.gsh        [d];
+        xferinfo[d].dst.lbnd        = data.lbnd       [d];
+        xferinfo[d].dst.lsh         = data.lsh        [d];
+        xferinfo[d].dst.lbbox       = fake_bbox       [2*d  ];
+        xferinfo[d].dst.ubbox       = fake_bbox       [2*d+1];
+        xferinfo[d].dst.nghostzones = data.nghostzones[d];
+        xferinfo[d].dst.off         = 0;
+        xferinfo[d].dst.str         = 1;
+        xferinfo[d].dst.len         = data.gsh        [d];
+        
+        xferinfo[d].xpose = d;
+        xferinfo[d].flip  = 0;
+      }
+      
+      switch (ndirs) {
+      case 1:
+        /* face */
+        for (q=0; q<1; ++q) {
+          xferinfo[otherdir[q]].src.off = stencil[otherdir[q]] + offset[otherdir[q]];
+          xferinfo[otherdir[q]].src.len = stencil[     dir[q]];
+          xferinfo[     dir[q]].dst.off = 0;
+          xferinfo[     dir[q]].dst.len = stencil[     dir[q]];
+          
+          xferinfo[     dir[q]].xpose = otherdir[q];
+          xferinfo[otherdir[q]].xpose =      dir[1];
+        }
+        break;
+      case 2:
+        /* edge */
+        for (q=0; q<1; ++q) {
+          xferinfo[otherdir[q]].src.off = stencil[otherdir[q]] + offset[otherdir[q]];
+          xferinfo[otherdir[q]].src.len = stencil[     dir[q]];
+          xferinfo[     dir[q]].dst.off = 0;
+          xferinfo[     dir[q]].dst.len = stencil[     dir[q]];
+          
+          xferinfo[dir[q]].flip = 1;
+        }
+        break;
+      default:
+        assert (0);
+      }
+      
+      ierr = Slab_Transfer
+        (cctkGH, group.dim, xferinfo, -1,
+         group.vartype, srcptr, group.vartype, varptr);
+      assert (!ierr);
+      
+      free (xferinfo);
+      
+    } /* if have_global_bbox */
+    
+    /* take parity into account */
+    have_local_bbox = 1;
+    for (q=0; q<ndirs; ++q) {
+      have_local_bbox = have_local_bbox && cctk_bbox[2*dir[q]];
+    }
+    if (have_local_bbox) {
+      assert (abs(parity) == 1);
+      if (parity == -1) {
+        int i, j, k;
+        assert (dir == 0);
+        assert (group.dim == 3);
+        assert (group.vartype == CCTK_VARIABLE_REAL);
+        for (k=0; k<xferinfo[2].dst.len; ++k) {
+          for (j=0; j<xferinfo[1].dst.len; ++j) {
+            for (i=0; i<xferinfo[0].dst.len; ++i) {
+              const int ind
+                = CCTK_GFINDEX3D(cctkGH,
+                                 xferinfo[0].dst.off + i - cctk_lbnd[0],
+                                 xferinfo[1].dst.off + j - cctk_lbnd[1],
+                                 xferinfo[2].dst.off + k - cctk_lbnd[2]);
+              ((CCTK_REAL *) varptr) [ind] *= -1;
+            }
+          }
+        }
+      }
+      
+    } /* if bbox */
+    
+  } /* for step */
+  
+  return 0;
+}
+
+
+
+void Rot90_ApplyBC (CCTK_ARGUMENTS)
+{
+  DECLARE_CCTK_ARGUMENTS;
+  
+  int nvars;
+  CCTK_INT * restrict indices;
+  CCTK_INT * restrict faces;
+  CCTK_INT * restrict widths;
+  CCTK_INT * restrict tables;
+  int vi;
+  int dim;
+  int * restrict stencil;
+  int i;
+  int ierr;
+  
+  assert (cctkGH);
+  
+  nvars = Boundary_SelectedGVs (cctkGH, 0, 0, 0, 0, 0, 0);
+  assert (nvars>=0);
+  
+  indices = malloc (nvars * sizeof *indices);
+  assert (indices);
+  faces = malloc (nvars * sizeof *faces);
+  assert (faces);
+  widths = malloc (nvars * sizeof *widths);
+  assert (widths);
+  tables = malloc (nvars * sizeof *tables);
+  assert (tables);
+  
+  ierr =  Boundary_SelectedGVs
+    (cctkGH, nvars, indices, faces, widths, tables, 0);
+  assert (ierr == nvars);
+  
+  for (i=0; i<nvars; ++i) {
+    vi = indices[i];
+    assert (vi>=0 && vi<CCTK_NumVars());
+    
+    assert (widths[i] >= 0);
+    
+    dim = CCTK_GroupDimFromVarI (vi);
+    assert (dim>=0);
+    
+    stencil = malloc (dim * sizeof *stencil);
+    assert (stencil);
+    ierr = CCTK_GroupnghostzonesVI (cctkGH, dim, stencil, vi);
+    assert (!ierr);
+    
+    ierr = BndRot90VI (cctkGH, stencil, vi);
+    assert (!ierr);
+    
+    free (stencil);
+  }
+  
+  free (indices);
+  free (faces);
+  free (widths);
+  free (tables);
+}