PCREDISTRIBUTE — PETSc 3.21.4 documentation

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# 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.

Supports the function `PCFieldSplitSetIS()`; pass the appropriate reduced field indices to an inner `PCFIELDSPLIT`, set with, for example `-ksp_type preonly -pc_type redistribute -redistribute_pc_type fieldsplit`. Does not support the `PCFIELDSPLIT` options database keys.

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.

The matrix block information is lost with the possible removal of individual rows and columns of the matrix, thus the behavior of the preconditioner on the reduced system may be very different (worse) than running that preconditioner on the full system. This is specifically true for elasticity problems.

## Developer Note

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

## See Also

KSP: Linear System Solvers, `PCCreate()`, `PCSetType()`, `PCType`, `PCRedistributeGetKSP()`, `MatZeroRows()`, `PCFieldSplitSetIS()`, `PCFIELDSPLIT`

## Level

intermediate

## Location

src/ksp/pc/impls/redistribute/redistribute.c

## Examples

src/ksp/ksp/tutorials/ex84.c

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