:orphan:
# ISEmbed
Embed `IS` `a` into `IS` `b` by finding the locations in `b` that have the same indices as in `a`. If `c` is the `IS` of these locations, we have `a = b*c`, regarded as a composition of the corresponding `ISLocalToGlobalMapping`. 
## Synopsis
```
#include "petscis.h"  
PetscErrorCode ISEmbed(IS a, IS b, PetscBool drop, IS *c)
```
Not Collective


## Input Parameters

- ***a    -*** `IS` to embed
- ***b    -*** `IS` to embed into
- ***drop -*** flag indicating whether to drop indices of `a` that are not in `b`.



## Output Parameter

- ***c    -*** local embedding indices





## Notes
If some of the global indices of `a` are not among the indices of `b`, the embedding is impossible. The local indices of `a`
corresponding to these global indices are either mapped to -1 (if `!drop`) or are omitted (if `drop`). In the former
case the size of `c` is the same as that of `a`, in the latter case the size of `c` may be smaller.

The resulting `IS` is sequential, since the index substitution it encodes is purely local.


## See Also
 `IS`, `ISLocalToGlobalMapping`

## Level
developer

## Location
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/vec/is/is/utils/isdiff.c.html#ISEmbed">src/vec/is/is/utils/isdiff.c</A>


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[Edit on GitLab](https://gitlab.com/petsc/petsc/-/edit/release/src/vec/is/is/utils/isdiff.c)


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