Hi,
I am solving a set of nonlinear and steady equations.
1.
Following ex13, I just create
LinearImplicitSystem & system =
equation_systems.add_system<LinearImplicitSystem>("axis");
is this correct? or should I creat something like:
NonlinearImplicitSystem & system =
equation_systems.add_system<LinearImplicitSystem>("axis"); ?
2. In ex13, I am not sure what the following code do. Are these the codes of
Newton's method for solving nonlinear equations? Usually, when choice
Newton's method, tangent stiffness matrix will be calcualated. But I can not
find the corresponding code for achieving this? Thanks in advance for your
kind help.
*for* (*unsigned* *int* l=0; l<n_nonlinear_steps; ++l)
{
last_nonlinear_soln->zero();
last_nonlinear_soln->add(*navier_stokes_system.solution);
perf_log.start_event(*"linear solve"*);
equation_systems.get_system(*"Navier-Stokes"*).solve();
perf_log.stop_event(*"linear solve"*);
last_nonlinear_soln->add (-1., *navier_stokes_system.solution);
last_nonlinear_soln->close();
*const* Real norm_delta = last_nonlinear_soln->l2_norm();
*const* *unsigned* *int* n_linear_iterations =
navier_stokes_system.n_linear_iterations();
*const* Real final_linear_residual =
navier_stokes_system.final_linear_residual();
*std*::cout << *"Linear solver converged at step: "*
<< n_linear_iterations
<< *", final residual: "*
<< final_linear_residual
<< *" Nonlinear convergence: ||u - u_old|| = "*
<< norm_delta
<< std::endl;
*if* ((norm_delta < nonlinear_tolerance) &&
(navier_stokes_system.final_linear_residual() < nonlinear_tolerance))
{
*std*::cout << *" Nonlinear solver converged at step "*
<< l
<< std::endl;
*break*;
}
equation_systems.parameters.set<Real> (*"linear solver tolerance"*) =
*Utility*::pow<2>(final_linear_residual);
} *// end nonlinear loop
*
*
*
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