PETSc version 3.16.5
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# KSPGMRESSetHapTol

Sets tolerance for determining happy breakdown in GMRES, FGMRES and LGMRES.

### Synopsis

    #include "petscksp.h"
    PetscErrorCode  KSPGMRESSetHapTol(KSP ksp,PetscReal tol)

Logically Collective on ksp

### Input Parameters

| ksp | - the Krylov space context
| tol | - the tolerance

### Options Database

| -ksp_gmres_haptol <positive real value>

Note: Happy breakdown is the rare case in GMRES where an 'exact' solution is obtained after a certain number of iterations. If you attempt more iterations after this point unstable things can happen hence very occasionally you may need to set this value to detect this condition

### See Also

KSPSetTolerances()

### Level

intermediate

### Location

src/ksp/ksp/impls/gmres/gmres.c

### Implementations

KSPGMRESSetHapTol_GMRES in src/ksp/ksp/impls/gmres/gmres.c
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