petsc-3.12.4 2020-02-04
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# KSPLSQRGetNorms

Get norm estimates that LSQR computes internally during KSPSolve().

### Synopsis

    #include "petscksp.h"
    PetscErrorCode  KSPLSQRGetNorms(KSP ksp,PetscReal *arnorm, PetscReal *anorm)

Not Collective

### Input Parameters

ksp -iterative context

### Output Parameters

| arnorm | - good estimate of norm((A*inv(Pmat))'*r), where r = A*x - b, used in specific stopping criterion
| anorm | - poor estimate of norm(A*inv(Pmat),'fro') used in specific stopping criterion

### Notes

Output parameters are meaningful only after KSPSolve(). These are the same quantities as normar and norma in MATLAB's lsqr(), whose output lsvec is a vector of normar / norma for all iterations. If -ksp_lsqr_exact_mat_norm is set or KSPLSQRSetExactMatNorm(ksp, PETSC_TRUE) called, then anorm is exact Frobenius norm.

### See Also

KSPSolve(), KSPLSQR, KSPLSQRSetExactMatNorm()

### Level

intermediate

### Location

src/ksp/ksp/impls/lsqr/lsqr.c
Index of all KSP routines
Table of Contents for all manual pages
Index of all manual pages