:orphan:
# 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)
```none
     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)
```none
     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


## See Also
 [PetscSection](sec_petscsection), `PetscSectionSym`, `PetscSectionRestorePointSyms()`, `PetscSectionSymCreate()`, `PetscSectionSetSym()`, `PetscSectionGetSym()`

## Level
developer

## Location
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/vec/is/section/interface/section.c.html#PetscSectionGetPointSyms">src/vec/is/section/interface/section.c</A>


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[Index of all PetscSection routines](index.md)  
[Table of Contents for all manual pages](/manualpages/index.md)  
[Index of all manual pages](/manualpages/singleindex.md)