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# 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}.

## See Also

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

## Level

beginner

## Location

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

## Examples

src/vec/vec/utils/tagger/tutorials/ex1.c
src/vec/is/is/tutorials/ex3.c
src/ksp/ksp/tutorials/ex71.c
src/vec/is/is/tutorials/ex3f90.F90

Index of all IS routines
Table of Contents for all manual pages
Index of all manual pages