petsc-3.15.0 2021-04-05
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# DMPlexSetClosurePermutationTensor

Create a permutation from the default (BFS) point ordering in the closure, to a lexicographic ordering over the tensor product cell (i.e., line, quad, hex, etc.), and set this permutation in the section provided (or the section of the DM).

### Synopsis

```#include "petscdmplex.h"
PetscErrorCode DMPlexSetClosurePermutationTensor(DM dm, PetscInt point, PetscSection section)
```

### Input Parameters

 dm - The DM point - Either a cell (highest dim point) or an edge (dim 1 point), or PETSC_DETERMINE section - The PetscSection to reorder, or NULL for the default section

Note: The point is used to determine the number of dofs/field on an edge. For SEM, this is related to the polynomial degree of the basis.

### Example

A typical interpolated single-quad mesh might order points as
```  [c0, v1, v2, v3, v4, e5, e6, e7, e8]

v4 -- e6 -- v3
|           |
e7    c0    e8
|           |
v1 -- e5 -- v2
```

(There is no significance to the ordering described here.) The default section for a Q3 quad might typically assign dofs in the order of points, e.g.,

```    c0 -> [0,1,2,3]
v1 -> [4]
...
e5 -> [8, 9]
```

which corresponds to the dofs

```    6   10  11  7
13  2   3   15
12  0   1   14
4   8   9   5
```

The closure in BFS ordering works through height strata (cells, edges, vertices) to produce the ordering

```  0 1 2 3 8 9 14 15 11 10 13 12 4 5 7 6
```

After calling DMPlexSetClosurePermutationTensor(), the closure will be ordered lexicographically,

```   4 8 9 5 12 0 1 14 13 2 3 15 6 10 11 7
```

DMGetLocalSection(), PetscSectionSetClosurePermutation(), DMSetGlobalSection()

developer

### Location

src/dm/impls/plex/plex.c

### Examples

src/dm/impls/plex/tutorials/ex6.c.html
src/dm/impls/plex/tutorials/ex8.c.html

Index of all DMPLEX routines