PETSc version 3.17.4
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# VecISAXPY

Adds a reduced vector to the appropriate elements of a full-space vector. vfull[is[i]] += alpha*vreduced[i]

### Synopsis

    #include "petscvec.h"
    PetscErrorCode VecISAXPY(Vec vfull, IS is, PetscScalar alpha, Vec vreduced)

### Input Parameters

| vfull | - the full-space vector
| is | - the index set for the reduced space
| alpha | - the scalar coefficient
| vreduced | - the reduced-space vector

### Output Parameters

| 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.

### See Also

VecAXPY(), VecGetOwnershipRange()

### Level

advanced

### Location

src/vec/vec/utils/projection.c
Index of all Vec routines
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