# PCREDISTRIBUTE
Redistributes a matrix for load balancing, removing the rows (and the corresponding columns) that only have a diagonal entry and then applies a `KSP` to that new smaller matrix 


## Notes
Options for the redistribute `KSP` and `PC` with the options database prefix -redistribute_

Usually run this with `-ksp_type preonly`

If you have used `MatZeroRows()` to eliminate (for example, Dirichlet) boundary conditions for a symmetric problem then you can use, for example, `-ksp_type preonly
-pc_type redistribute -redistribute_ksp_type cg -redistribute_pc_type bjacobi -redistribute_sub_pc_type icc` to take advantage of the symmetry.

This does NOT call a partitioner to reorder rows to lower communication; the ordering of the rows in the original matrix and redistributed matrix is the same. Rows are moved
between MPI processes inside the preconditioner to balance the number of rows on each process.


## Developer Note
Should add an option to this preconditioner to use a partitioner to redistribute the rows to lower communication.


## See Also
 `PCCreate()`, `PCSetType()`, `PCType`, `PCRedistributeGetKSP()`, `MatZeroRows()`

## Level
intermediate

## Location
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/pc/impls/redistribute/redistribute.c.html#PCREDISTRIBUTE">src/ksp/pc/impls/redistribute/redistribute.c</A>


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[Edit on GitLab](https://gitlab.com/petsc/petsc/-/edit/release/src/ksp/pc/impls/redistribute/redistribute.c)


[Index of all PC routines](index.md)  
[Table of Contents for all manual pages](/docs/manualpages/index.md)  
[Index of all manual pages](/docs/manualpages/singleindex.md)  
