petsc-3.12.4 2020-02-04
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# ISLocalToGlobalMappingCreate

Creates a mapping between a local (0 to n) ordering and a global parallel ordering.

### Synopsis

    #include "petscis.h"
    PetscErrorCode  ISLocalToGlobalMappingCreate(MPI_Comm comm,PetscInt bs,PetscInt n,const PetscInt indices[],PetscCopyMode mode,ISLocalToGlobalMapping *mapping)

Not Collective, but communicator may have more than one process

### Input Parameters

| comm | - MPI communicator
| bs | - the block size
| n | - the number of local elements divided by the block size, or equivalently the number of block indices
| indices | - the global index for each local element, these do not need to be in increasing order (sorted), these values should not be scaled (i.e. multiplied) by the blocksize bs
| mode | - see PetscCopyMode

### Output Parameter

mapping -new mapping data structure

### Notes

There is one integer value in indices per block and it represents the actual indices bs*idx + j, where j=0,..,bs-1

For "small" problems when using ISGlobalToLocalMappingApply() and ISGlobalToLocalMappingApplyBlock(), the ISLocalToGlobalMappingType of ISLOCALTOGLOBALMAPPINGBASIC will be used; this uses more memory but is faster; this approach is not scalable for extremely large mappings. For large problems ISLOCALTOGLOBALMAPPINGHASH is used, this is scalable. Use ISLocalToGlobalMappingSetType() or call ISLocalToGlobalMappingSetFromOptions() with the option -islocaltoglobalmapping_type <basic,hash> to control which is used.

### See Also

ISLocalToGlobalMappingDestroy(), ISLocalToGlobalMappingCreateIS(), ISLocalToGlobalMappingSetFromOptions(), ISLOCALTOGLOBALMAPPINGBASIC, ISLOCALTOGLOBALMAPPINGHASH
ISLocalToGlobalMappingSetType(), ISLocalToGlobalMappingType

### Level

advanced

### Location

src/vec/is/utils/isltog.c

### Examples

src/vec/vec/examples/tutorials/ex8.c.html
src/vec/is/is/examples/tutorials/ex4.c.html
src/vec/is/is/examples/tutorials/ex5.c.html
src/ksp/ksp/examples/tutorials/ex59.c.html
Index of all IS routines
Table of Contents for all manual pages
Index of all manual pages