# ISCreateBlock#

Creates a data structure for an index set containing a list of integers. Each integer represents a fixed block size set of indices.

## Synopsis#

#include "petscis.h"
PetscErrorCode ISCreateBlock(MPI_Comm comm, PetscInt bs, PetscInt n, const PetscInt idx[], PetscCopyMode mode, IS *is)


Collective

## Input Parameters#

• comm - the MPI communicator

• bs - number of elements in each block

• n - the length of the index set (the number of blocks)

• idx - the list of integers, one for each block, the integers contain the index of the first entry of each block divided by the block size

• mode - see PetscCopyMode, only PETSC_COPY_VALUES and PETSC_OWN_POINTER are supported in this routine

## Output Parameter#

• is - the new index set

## Notes#

When the communicator is not MPI_COMM_SELF, the operations on the index sets, IS, are NOT conceptually the same as MPI_Group operations. The index sets are then distributed sets of indices and thus certain operations on them are collective.

The routine ISBlockSetIndices() can be used to provide the indices to a preexisting block IS

## Example#

If you wish to index the values {0,1,6,7}, then use a block size of 2 and idx of {0,3}.

Low-level Vector Communication, IS, ISCreateStride(), ISCreateGeneral(), ISAllGather(), ISBlockSetIndices(), ISBLOCK, ISGENERAL

beginner

## Location#

src/vec/is/is/impls/block/block.c

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