Krylov parameters

Asked by Ángel Javier Omella Milián on 2013-05-14

Hi, I'm new but I hope to do it properly...
I'm trying to solve a problem but I can not control the parameters of the solver... in dolfin 1.1.0

 focusing on the problem:

 problem = LinearVariationalProblem(a, L, u, bcs)
    solver = LinearVariationalSolver(problem)
    solver.parameters['linear_solver'] = 'gmres'
    solver.parameters['preconditioner'] = 'jacobi'
    prm = solver.parameters['krylov_solver']
    prm['absolute_tolerance'] = 1E-9
    prm['relative_tolerance'] = 1E-7
    prm['maximum_iterations'] = 10
    prm ['gmres']['restart']= 7
    prm["monitor_convergence"] = True
    prm["error_on_nonconvergence"] = True

    info(solver.parameters, True)


...It runs ok and tells me...

  Solving linear variational problem.
  Applying boundary conditions to linear system.
  Applying boundary conditions to linear system.
  Solving linear system of size 3298 x 3298 (PETSc Krylov solver).
  PETSc Krylov solver starting to solve 3298 x 3298 system.
  PETSc Krylov solver (gmres, jacobi) converged in 169 iterations.

If I fixed maximum_iterations to 10,
Why my problem converged? Why do not solver stops in 10 iterations and diverge? Why it runs to 169 iterations?
When I read info parameters, the values are ok, but later the solver are not taking into account these parameters!!

When I change absolute and relative tolerance the number of iterations remains constant... in 169, obtaining the same result...
it not runs well...

I would be very grateful if someone could tell me what I'm doing wrong or explain me what is happening??


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Johannes Ring (johannr) said : #1

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