petsc-3.14.5 2021-03-03
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# ISIdentity

Determines whether index set is the identity mapping.

### Synopsis

    #include "petscis.h"
    PetscErrorCode  ISIdentity(IS is,PetscBool  *ident)

Collective on IS

### Input Parmeters

| is | - the index set

### Output Parameters

| ident | - PETSC_TRUE if an identity, else PETSC_FALSE

Note: If ISSetIdentity() (or ISSetInfo() for a permanent property) has been called, ISIdentity() will return its answer without communication between processes, but otherwise the output ident will be computed from ISGetInfo(), which may require synchronization on the communicator of IS. To avoid this computation, call ISGetInfo() directly with the compute flag set to PETSC_FALSE, and ident will be assumed false.

### See Also

ISSetIdentity(), ISGetInfo()

### Level

intermediate

### Location

src/vec/is/is/interface/index.c
Index of all IS routines
Table of Contents for all manual pages
Index of all manual pages