:orphan:
# VecISCopy
Copies between a reduced vector and the appropriate elements of a full-space vector. 
## Synopsis
```
#include "petscvec.h"  
PetscErrorCode VecISCopy(Vec vfull, IS is, ScatterMode mode, Vec vreduced)
```

## Input Parameters

- ***vfull    -*** the full-space vector
- ***is       -*** the index set for the reduced space
- ***mode     -*** the direction of copying, `SCATTER_FORWARD` or `SCATTER_REVERSE`
- ***vreduced -*** the reduced-space vector



## Output Parameter

- ***vfull    -*** the sum of the full-space vector and reduced-space vector





## Notes
The index set identifies entries in the global vector.
Negative indices are skipped; indices outside the ownership range of `vfull` will raise an error.
```none
    mode == SCATTER_FORWARD: vfull[is[i]] = vreduced[i]
    mode == SCATTER_REVERSE: vreduced[i] = vfull[is[i]]
```



## See Also
 `VecISSet()`, `VecISAXPY()`, `VecCopy()`

## Level
advanced

## Location
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/vec/vec/utils/projection.c.html#VecISCopy">src/vec/vec/utils/projection.c</A>

## Examples
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/snes/tutorials/ex13.c.html">src/snes/tutorials/ex13.c</A><BR>


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


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