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# PCQR

Uses a direct solver, based on QR factorization, as a preconditioner

## Note

Usually this will compute an “exact” solution in one iteration and does not need a Krylov method (i.e. you can use -ksp_type preonly, or `KSPSetType`(ksp,`KSPPREONLY`) for the Krylov method

## See Also

KSP: Linear System Solvers, `PCCreate()`, `PCSetType()`, `PCType`, `PC`, `PCSVD`, `PCILU`, `PCLU`, `PCCHOLESKY`, `PCICC`, `PCFactorSetReuseOrdering()`, `PCFactorSetReuseFill()`, `PCFactorGetMatrix()`, `PCFactorSetFill()`, `PCFactorSetUseInPlace()`, `PCFactorSetMatOrderingType()`, `PCFactorSetColumnPivot()`, `PCFactorSetPivotingInBlocks()`, `PCFactorSetShiftType()`, `PCFactorSetShiftAmount()` `PCFactorReorderForNonzeroDiagonal()`

## Level

beginner

## Location

src/ksp/pc/impls/factor/qr/qr.c

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