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# PCQR

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

## Notes

This is usually used as a preconditioner for `KSPLSQR`

If the matrix used to construct the preconditioner is a `MATNORMAL` or `MATNORMALHERMITIAN` matrix, then the QR is performed on the inner matrix to provide the preconditioner.

## 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()`, `KSPLSQR`

## 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