petsc-master 2014-11-25
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KSPSetFromOptions

Sets KSP options from the options database. This routine must be called before KSPSetUp() if the user is to be allowed to set the Krylov type.

Synopsis

#include "petscksp.h" 
PetscErrorCode  KSPSetFromOptions(KSP ksp)
Collective on KSP

Input Parameters

ksp -the Krylov space context

Options Database Keys

-ksp_max_it - maximum number of linear iterations
-ksp_rtol rtol - relative tolerance used in default determination of convergence, i.e. if residual norm decreases by this factor than convergence is declared
-ksp_atol abstol - absolute tolerance used in default convergence test, i.e. if residual norm is less than this then convergence is declared
-ksp_divtol tol - if residual norm increases by this factor than divergence is declared
-ksp_converged_use_initial_residual_norm - see KSPConvergedDefaultSetUIRNorm()
-ksp_converged_use_min_initial_residual_norm - see KSPConvergedDefaultSetUMIRNorm()
-ksp_norm_type - none - skip norms used in convergence tests (useful only when not using convergence test (say you always want to run with 5 iterations) to save on communication overhead preconditioned - default for left preconditioning unpreconditioned - see KSPSetNormType() natural - see KSPSetNormType()
-ksp_check_norm_iteration it - do not compute residual norm until iteration number it (does compute at 0th iteration) works only for PCBCGS, PCIBCGS and and PCCG
-ksp_lag_norm - compute the norm of the residual for the ith iteration on the i+1 iteration; this means that one can use the norm of the residual for convergence test WITHOUT an extra MPI_Allreduce() limiting global synchronizations. This will require 1 more iteration of the solver than usual.
-ksp_fischer_guess <model,size> - uses the Fischer initial guess generator for repeated linear solves
-ksp_constant_null_space - assume the operator (matrix) has the constant vector in its null space
-ksp_test_null_space - tests the null space set with KSPSetNullSpace() to see if it truly is a null space
-ksp_knoll - compute initial guess by applying the preconditioner to the right hand side
-ksp_monitor_cancel - cancel all previous convergene monitor routines set
-ksp_monitor <optional filename> - print residual norm at each iteration
-ksp_monitor_lg_residualnorm - plot residual norm at each iteration
-ksp_monitor_solution - plot solution at each iteration
-ksp_monitor_singular_value - monitor extreme singular values at each iteration

Notes

To see all options, run your program with the -help option or consult Users-Manual: Chapter 4 KSP: Linear Equations Solvers

Keywords

KSP, set, from, options, database

See Also

KSPSetUseFischerGuess()

Level:beginner
Location:
src/ksp/ksp/interface/itcl.c
Index of all KSP routines
Table of Contents for all manual pages
Index of all manual pages

Examples

src/ksp/pc/examples/tutorials/ex1.c.html
src/ksp/pc/examples/tutorials/ex2.c.html
src/ksp/ksp/examples/tutorials/ex1.c.html
src/ksp/ksp/examples/tutorials/ex2.c.html
src/ksp/ksp/examples/tutorials/ex3.c.html
src/ksp/ksp/examples/tutorials/ex4.c.html
src/ksp/ksp/examples/tutorials/ex5.c.html
src/ksp/ksp/examples/tutorials/ex7.c.html
src/ksp/ksp/examples/tutorials/ex8.c.html
src/ksp/ksp/examples/tutorials/ex8g.c.html
src/ksp/ksp/examples/tutorials/ex9.c.html