petsc-3.7.7 2017-09-25
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# PCBJACOBI

Use block Jacobi preconditioning, each block is (approximately) solved with its own KSP object.

### Options Database Keys

-pc_use_amat -use Amat to apply block of operator in inner Krylov method

Notes: Each processor can have one or more blocks, but a block cannot be shared by more than one processor. Defaults to one block per processor.

To set options on the solvers for each block append -sub_ to all the KSP, KSP, and PC options database keys. For example, -sub_pc_type ilu -sub_pc_factor_levels 1 -sub_ksp_type preonly

To set the options on the solvers separate for each block call PCBJacobiGetSubKSP() and set the options directly on the resulting KSP object (you can access its PC KSPGetPC())

For CUSP vectors it is recommended to use exactly one block per MPI process for best performance. Different block partitioning may lead to additional data transfers between host and GPU that lead to degraded performance.

### See Also

PCCreate(), PCSetType(), PCType (for list of available types), PC,
PCASM, PCSetUseAmat(), PCGetUseAmat(), PCBJacobiGetSubKSP(), PCBJacobiSetTotalBlocks(), PCBJacobiSetLocalBlocks(), PCSetModifySubmatrices()

Level:beginner
Location:src/ksp/pc/impls/bjacobi/bjacobi.c
Index of all PC routines
Table of Contents for all manual pages
Index of all manual pages

### Examples

src/ksp/ksp/examples/tutorials/ex7.c.html