# VecSetOption#

Sets an option for controling a vector’s behavior.

## Synopsis#

#include "petscvec.h"
PetscErrorCode VecSetOption(Vec x, VecOption op, PetscBool flag)


Collective

## Input Parameters#

• x - the vector

• op - the option

• flag - turn the option on or off

## Supported Options#

• VEC_IGNORE_OFF_PROC_ENTRIES, which causes VecSetValues() to ignore- entries destined to be stored on a separate processor. This can be used to eliminate the global reduction in the VecAssemblyBegin() if you know that you have only used VecSetValues() to set local elements

• VEC_IGNORE_NEGATIVE_INDICES, which means you can pass negative indices- in ix in calls to VecSetValues() or VecGetValues(). These rows are simply ignored.

• VEC_SUBSET_OFF_PROC_ENTRIES, which causes VecAssemblyBegin() to assume that the off- process entries will always be a subset (possibly equal) of the off-process entries set on the first assembly which had a true VEC_SUBSET_OFF_PROC_ENTRIES and the vector has not changed this flag afterwards. If this assembly is not such first assembly, then this assembly can reuse the communication pattern setup in that first assembly, thus avoiding a global reduction. Subsequent assemblies setting off-process values should use the same InsertMode as the first assembly.

## Developer Note#

The InsertMode restriction could be removed by packing the stash messages out of place.

Vectors and Parallel Data, Vec, VecSetValues()

intermediate

## Location#

src/vec/vec/interface/vector.c

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