# DMStagPopulateLocalToGlobalInjective
populate an internal 1-to-1 local-to-global map 
## Synopsis
```
PetscErrorCode DMStagPopulateLocalToGlobalInjective(DM dm)
```
Collective

Creates an internal object which explicitly maps a single local degree of
freedom to each global degree of freedom. This is used, if populated,
instead of SCATTER_REVERSE_LOCAL with the (1-to-many, in general)
global-to-local map, when DMLocalToGlobal() is called with INSERT_VALUES.
This allows usage, for example, even in the periodic, 1-rank case, where
the inverse of the global-to-local map, even when restricted to on-rank
communication, is non-injective. This is at the cost of storing an additional
VecScatter object inside each `DMSTAG` object.


## Input Parameter

- ***dm -*** the `DMSTAG` object





## Notes
In normal usage, library users shouldn't be concerned with this function,
as it is called during `DMSetUp()`, when required.

Returns immediately if the internal map is already populated.


## Developer Notes
This could, if desired, be moved up to a general `DM` routine. It would allow,
for example, `DMDA` to support `DMLocalToGlobal()` with `INSERT_VALUES`,
even in the single-rank periodic case.


## See Also
 [](chapter_stag), `DMSTAG`, `DMLocalToGlobal()`, `VecScatter`

## Level
developer

## Location
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/dm/impls/stag/stagutils.c.html#DMStagPopulateLocalToGlobalInjective">src/dm/impls/stag/stagutils.c</A>

## Implementations

<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/dm/impls/stag/stag1d.c.html#DMStagPopulateLocalToGlobalInjective_1d">DMStagPopulateLocalToGlobalInjective_1d in src/dm/impls/stag/stag1d.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/dm/impls/stag/stag2d.c.html#DMStagPopulateLocalToGlobalInjective_2d">DMStagPopulateLocalToGlobalInjective_2d in src/dm/impls/stag/stag2d.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/dm/impls/stag/stag3d.c.html#DMStagPopulateLocalToGlobalInjective_3d">DMStagPopulateLocalToGlobalInjective_3d in src/dm/impls/stag/stag3d.c</A><BR>


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[Edit on GitLab](https://gitlab.com/petsc/petsc/-/edit/release/src/dm/impls/stag/stagutils.c)


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