PetscSectionGetPointSyms#

Get the symmetries for a set of points in a PetscSection under specific orientations.

Synopsis#

#include "petscsection.h"   
PetscErrorCode PetscSectionGetPointSyms(PetscSection section, PetscInt numPoints, const PetscInt *points, const PetscInt ***perms, const PetscScalar ***rots)

Not Collective

Input Parameters#

section - the section
numPoints - the number of points
points - an array of size 2 * numPoints, containing a list of (point, orientation) pairs. (An orientation is an arbitrary integer: its interpretation is up to sym. Orientations are used by DM: for their interpretation in that context, see DMPlexGetConeOrientation()).

Output Parameters#

perms - The permutations for the given orientations (or NULL if there is no symmetry or the permutation is the identity).
rots - The field rotations symmetries for the given orientations (or NULL if there is no symmetry or the rotations are all identity).

Example of usage, gathering dofs into a local array (lArray) from a section array (sArray)#

     const PetscInt    **perms;
     const PetscScalar **rots;
     PetscInt            lOffset;

     PetscSectionGetPointSyms(section,numPoints,points,&perms,&rots);
     for (i = 0, lOffset = 0; i < numPoints; i++) {
       PetscInt           point = points[2*i], dof, sOffset;
       const PetscInt    *perm  = perms ? perms[i] : NULL;
       const PetscScalar *rot   = rots  ? rots[i]  : NULL;

       PetscSectionGetDof(section,point,&dof);
       PetscSectionGetOffset(section,point,&sOffset);

       if (perm) {for (j = 0; j < dof; j++) {lArray[lOffset + perm[j]]  = sArray[sOffset + j];}}
       else      {for (j = 0; j < dof; j++) {lArray[lOffset +      j ]  = sArray[sOffset + j];}}
       if (rot)  {for (j = 0; j < dof; j++) {lArray[lOffset +      j ] *= rot[j];             }}
       lOffset += dof;
     }
     PetscSectionRestorePointSyms(section,numPoints,points,&perms,&rots);

Example of usage, adding dofs into a section array (sArray) from a local array (lArray)#

     const PetscInt    **perms;
     const PetscScalar **rots;
     PetscInt            lOffset;

     PetscSectionGetPointSyms(section,numPoints,points,&perms,&rots);
     for (i = 0, lOffset = 0; i < numPoints; i++) {
       PetscInt           point = points[2*i], dof, sOffset;
       const PetscInt    *perm  = perms ? perms[i] : NULL;
       const PetscScalar *rot   = rots  ? rots[i]  : NULL;

       PetscSectionGetDof(section,point,&dof);
       PetscSectionGetOffset(section,point,&sOff);

       if (perm) {for (j = 0; j < dof; j++) {sArray[sOffset + j] += lArray[lOffset + perm[j]] * (rot ? PetscConj(rot[perm[j]]) : 1.);}}
       else      {for (j = 0; j < dof; j++) {sArray[sOffset + j] += lArray[lOffset +      j ] * (rot ? PetscConj(rot[     j ]) : 1.);}}
       offset += dof;
     }
     PetscSectionRestorePointSyms(section,numPoints,points,&perms,&rots);

Notes#

PetscSectionSetSym() must have been previously called to provide the symmetries to the PetscSection

Use PetscSectionRestorePointSyms() when finished with the data

Level#

developer

Location#

src/vec/is/section/interface/section.c

Index of all PetscSection routines
Table of Contents for all manual pages
Index of all manual pages