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mfem/examples/sundials/ex16.cpp
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// MFEM Example 16
// SUNDIALS Modification
//
// Compile with:
// make ex16 (GNU make)
// make sundials_ex16 (CMake)
//
// Sample runs: ex16
// ex16 -m ../../data/inline-tri.mesh
// ex16 -m ../../data/disc-nurbs.mesh -tf 2
// ex16 -s 12 -a 0.0 -k 1.0
// ex16 -s 15 -a 0.0 -k 1.0
// ex16 -s 8 -a 1.0 -k 0.0 -dt 1e-4 -tf 5e-2 -vs 25
// ex16 -s 11 -a 1.0 -k 0.0 -dt 1e-4 -tf 5e-2 -vs 25
// ex16 -s 9 -a 0.5 -k 0.5 -o 4 -dt 1e-4 -tf 2e-2 -vs 25
// ex16 -s 12 -a 0.5 -k 0.5 -o 4 -dt 1e-4 -tf 2e-2 -vs 25
// ex16 -s 10 -dt 1.0e-4 -tf 4.0e-2 -vs 40
// ex16 -s 13 -dt 1.0e-4 -tf 4.0e-2 -vs 40
// ex16 -m ../../data/fichera-q2.mesh
// ex16 -m ../../data/escher.mesh
// ex16 -m ../../data/beam-tet.mesh -tf 10 -dt 0.1
// ex16 -m ../../data/amr-quad.mesh -o 4 -r 0
// ex16 -m ../../data/amr-hex.mesh -o 2 -r 0
//
// Description: This example solves a time dependent nonlinear heat equation
// problem of the form du/dt = C(u), with a non-linear diffusion
// operator C(u) = \nabla \cdot (\kappa + \alpha u) \nabla u.
//
// The example demonstrates the use of nonlinear operators (the
// class ConductionOperator defining C(u)), as well as their
// implicit time integration. Note that implementing the method
// ConductionOperator::ImplicitSolve is the only requirement for
// high-order implicit (SDIRK) time integration. By default, this
// example uses the SUNDIALS ODE solvers from CVODE and ARKODE.
//
// We recommend viewing examples 2, 9 and 10 before viewing this
// example.
#include "mfem.hpp"
#include <fstream>
#include <iostream>
using namespace std;
using namespace mfem;
/** After spatial discretization, the conduction model is expressed as
*
* M du/dt = - K(u) u
*
* where u is the vector representing the temperature, M is the mass matrix,
* and K(u) is the diffusion operator with diffusivity depending on u:
* (\kappa + \alpha u).
*
* Class ConductionOperatorOperator represents the above ODE operator in the
* general form F(u, k, t) = G(u, t) where
*
* 1. F(u, du/dt, t) = du/dt (ODE is expressed in EXPLICIT form)
* G(u, t) = - inv(M) K(u) u
* 2. F(u, du/dt, t) = M du/dt (ODE is expressed in IMPLICIT form)
* G(u, t) = - K(u) u
*/
class ConductionOperator : public TimeDependentOperator
{
FiniteElementSpace &fespace;
Array<int> ess_tdof_list; // this list remains empty for pure Neumann b.c.
BilinearForm M;
SparseMatrix Mmat;
const real_t alpha, kappa;
std::unique_ptr<BilinearForm> K;
SparseMatrix Kmat;
std::unique_ptr<SparseMatrix> T; // T = M + gam K(u)
CGSolver M_solver; // Krylov solver for inverting the mass matrix M
DSmoother M_prec; // Preconditioner for the mass matrix M
CGSolver T_solver; // Implicit solver for T = M + gam K(u)
DSmoother T_prec; // Preconditioner for the implicit solver
mutable Vector z; // auxiliary vector
public:
ConductionOperator(FiniteElementSpace &f, const real_t alpha,
const real_t kappa, const Vector &u,
const Type &ode_expression_type);
// Compute K(u_n) for use as an approximation in - K(u) u
void SetConductionTensor(const Vector &u);
/** Compute G(u, t) as defined in the IMPLICIT expression form of the ODE
operator, i.e., @a v = - K(u_n) @a u. Note that K(u_n) is an
approximation to K(u). */
void ExplicitMult(const Vector &u, Vector &v) const override;
/** Solve for k in F(u, k, t) = G(u, t) for either EXPLICIT or IMPLICIT
expression forms of the ODE operator, i.e., @a k = - inv(M) K(u_n) @a u.
Note that K(u_n) is an approximation to K(u). */
void Mult(const Vector &u, Vector &k) const override;
/** Solve for k in F(u + gam*k, k, t) = G(u + gam*k, t) for either EXPLICIT
or IMPLICIT expression forms of the ODE operator, i.e.,
[ M + @a gam K(u_n) ] @a k = - K(u_n) @a u . Note that K(u_n) is an
approximation to K(u). */
void ImplicitSolve(const real_t gam, const Vector &u, Vector &k) override;
/** Setup to solve for dk in [dF/dk + gam*dF/du - gam*dG/du] dk = G - F for
either EXPLICIT or IMPLICIT expression forms of the ODE operator, i.e.,
[M - @a gam Jf(u)] dk = G - F, where Jf(u) is an approximation of the
Jacobian of -K(u) u. The approximation chosen here is Jf(u) = -K(u_n). */
int SUNImplicitSetup(const Vector &u, const Vector &fu, int jok, int *jcur,
real_t gam) override;
/** Solve for @a dk in the system in SUNImplicitSetup to the given tolerance,
with the residual @a r providing either
1. @a r = G - F = inv(M) f(u) - k (EXPLICIT expression form)
1. @a r = G - F = f(u) - M k (IMPLICIT expression form)
*/
int SUNImplicitSolve(const Vector &r, Vector &dk, real_t tol) override;
int SUNMassSetup() override;
int SUNMassSolve(const Vector &b, Vector &x, real_t tol) override;
int SUNMassMult(const Vector &x, Vector &v) override;
};
real_t InitialTemperature(const Vector &x)
{
if (x.Norml2() < 0.5)
{
return 2.0;
}
else
{
return 1.0;
}
}
int main(int argc, char *argv[])
{
// 0. Initialize SUNDIALS.
Sundials::Init();
// 1. Parse command-line options.
const char *mesh_file = "../../data/star.mesh";
int ref_levels = 2;
int order = 2;
int ode_solver_type = 9; // CVODE implicit BDF
real_t t_final = 0.5;
real_t dt = 1.0e-2;
real_t alpha = 1.0e-2;
real_t kappa = 0.5;
bool visualization = true;
bool visit = false;
int vis_steps = 5;
// Relative and absolute tolerances for CVODE and ARKODE.
const real_t reltol = 1e-4, abstol = 1e-4;
int precision = 8;
cout.precision(precision);
OptionsParser args(argc, argv);
args.AddOption(&mesh_file, "-m", "--mesh",
"Mesh file to use.");
args.AddOption(&ref_levels, "-r", "--refine",
"Number of times to refine the mesh uniformly.");
args.AddOption(&order, "-o", "--order",
"Order (degree) of the finite elements.");
args.AddOption(&ode_solver_type, "-s", "--ode-solver",
"ODE solver:\n\t"
"1 - Forward Euler,\n\t"
"2 - RK2,\n\t"
"3 - RK3 SSP,\n\t"
"4 - RK4,\n\t"
"5 - Backward Euler,\n\t"
"6 - SDIRK 2,\n\t"
"7 - SDIRK 3,\n\t"
"8 - CVODE (implicit Adams),\n\t"
"9 - CVODE (implicit BDF),\n\t"
"10 - ARKODE (default explicit),\n\t"
"11 - ARKODE (explicit Fehlberg-6-4-5),\n\t"
"12 - ARKODE (default implicit),\n\t"
"13 - ARKODE (default explicit with MFEM mass solve),\n\t"
"14 - ARKODE (explicit Fehlberg-6-4-5 with MFEM mass solve),\n\t"
"15 - ARKODE (default implicit with MFEM mass solve).");
args.AddOption(&t_final, "-tf", "--t-final",
"Final time; start time is 0.");
args.AddOption(&dt, "-dt", "--time-step",
"Time step.");
args.AddOption(&alpha, "-a", "--alpha",
"Alpha coefficient.");
args.AddOption(&kappa, "-k", "--kappa",
"Kappa coefficient offset.");
args.AddOption(&visualization, "-vis", "--visualization", "-no-vis",
"--no-visualization",
"Enable or disable GLVis visualization.");
args.AddOption(&visit, "-visit", "--visit-datafiles", "-no-visit",
"--no-visit-datafiles",
"Save data files for VisIt (visit.llnl.gov) visualization.");
args.AddOption(&vis_steps, "-vs", "--visualization-steps",
"Visualize every n-th timestep.");
args.Parse();
if (!args.Good())
{
args.PrintUsage(cout);
return 1;
}
args.PrintOptions(cout);
bool use_mass_solver = ode_solver_type >= 13;
// 2. Read the mesh from the given mesh file. We can handle triangular,
// quadrilateral, tetrahedral and hexahedral meshes with the same code.
std::unique_ptr<Mesh> mesh(new Mesh(mesh_file, 1, 1));
int dim = mesh->Dimension();
// 3. Refine the mesh to increase the resolution. In this example we do
// 'ref_levels' of uniform refinement, where 'ref_levels' is a
// command-line parameter.
for (int lev = 0; lev < ref_levels; lev++)
{
mesh->UniformRefinement();
}
// 4. Define the vector finite element space representing the current and the
// initial temperature, u_ref.
H1_FECollection fe_coll(order, dim);
FiniteElementSpace fespace(mesh.get(), &fe_coll);
int fe_size = fespace.GetTrueVSize();
cout << "Number of temperature unknowns: " << fe_size << endl;
GridFunction u_gf(&fespace);
// 5. Set the initial conditions for u. All boundaries are considered
// natural.
FunctionCoefficient u_0(InitialTemperature);
u_gf.ProjectCoefficient(u_0);
Vector u;
u_gf.GetTrueDofs(u);
// 6. Initialize the conduction ODE operator and the visualization.
ConductionOperator::Type ode_expression_type;
if (use_mass_solver)
{
ode_expression_type = ConductionOperator::Type::IMPLICIT;
}
else
{
ode_expression_type = ConductionOperator::Type::EXPLICIT;
}
ConductionOperator oper(fespace, alpha, kappa, u, ode_expression_type);
u_gf.SetFromTrueDofs(u);
{
ofstream omesh("ex16.mesh");
omesh.precision(precision);
mesh->Print(omesh);
ofstream osol("ex16-init.gf");
osol.precision(precision);
u_gf.Save(osol);
}
VisItDataCollection visit_dc("Example16", mesh.get());
visit_dc.RegisterField("temperature", &u_gf);
if (visit)
{
visit_dc.SetCycle(0);
visit_dc.SetTime(0.0);
visit_dc.Save();
}
socketstream sout;
if (visualization)
{
char vishost[] = "localhost";
int visport = 19916;
sout.open(vishost, visport);
if (!sout)
{
cout << "Unable to connect to GLVis server at "
<< vishost << ':' << visport << endl;
visualization = false;
cout << "GLVis visualization disabled.\n";
}
else
{
sout.precision(precision);
sout << "solution\n" << *mesh << u_gf;
sout << "pause\n";
sout << flush;
cout << "GLVis visualization paused."
<< " Press space (in the GLVis window) to resume it.\n";
}
}
// 7. Define the ODE solver used for time integration.
real_t t = 0.0;
std::unique_ptr<ODESolver> ode_solver;
switch (ode_solver_type)
{
// MFEM explicit methods
case 1: ode_solver = std::make_unique<ForwardEulerSolver>(); break;
case 2: ode_solver = std::make_unique<RK2Solver>(0.5); break; // midpoint method
case 3: ode_solver = std::make_unique<RK3SSPSolver>(); break;
case 4: ode_solver = std::make_unique<RK4Solver>(); break;
// MFEM implicit L-stable methods
case 5: ode_solver = std::make_unique<BackwardEulerSolver>(); break;
case 6: ode_solver = std::make_unique<SDIRK23Solver>(2); break;
case 7: ode_solver = std::make_unique<SDIRK33Solver>(); break;
// CVODE
case 8:
case 9:
{
int cvode_solver_type;
if (ode_solver_type == 8)
{
cvode_solver_type = CV_ADAMS;
}
else
{
cvode_solver_type = CV_BDF;
}
std::unique_ptr<CVODESolver> cvode(new CVODESolver(cvode_solver_type));
cvode->Init(oper);
cvode->SetSStolerances(reltol, abstol);
cvode->SetMaxStep(dt);
ode_solver = std::move(cvode);
break;
}
// ARKODE
case 10:
case 11:
case 12:
case 13:
case 14:
case 15:
{
ARKStepSolver::Type arkode_solver_type;
if (ode_solver_type == 12 || ode_solver_type == 15)
{
arkode_solver_type = ARKStepSolver::IMPLICIT;
}
else
{
arkode_solver_type = ARKStepSolver::EXPLICIT;
}
std::unique_ptr<ARKStepSolver> arkode(
new ARKStepSolver(arkode_solver_type));
arkode->Init(oper);
arkode->SetSStolerances(reltol, abstol);
arkode->SetMaxStep(dt);
if (ode_solver_type == 11 || ode_solver_type == 14)
{
arkode->SetERKTableNum(ARKODE_FEHLBERG_13_7_8);
}
if (use_mass_solver)
{
arkode->UseMFEMMassLinearSolver(SUNFALSE);
}
ode_solver = std::move(arkode);
break;
}
default:
cout << "Unknown ODE solver type: " << ode_solver_type << '\n';
return 3;
}
// Initialize MFEM integrators, SUNDIALS integrators are initialized above
if (ode_solver_type < 8) { ode_solver->Init(oper); }
// Since we want to update the diffusion coefficient after every time step,
// we need to use the "one-step" mode of the SUNDIALS solvers.
if (CVODESolver* cvode = dynamic_cast<CVODESolver*>(ode_solver.get()))
{
cvode->SetStepMode(CV_ONE_STEP);
}
else if (ARKStepSolver* arkode = dynamic_cast<ARKStepSolver*>(ode_solver.get()))
{
arkode->SetStepMode(ARK_ONE_STEP);
}
// 8. Perform time-integration (looping over the time iterations, ti, with a
// time-step dt).
cout << "Integrating the ODE ..." << endl;
tic_toc.Clear();
tic_toc.Start();
bool last_step = false;
for (int ti = 1; !last_step; ti++)
{
real_t dt_real = min(dt, t_final - t);
// Note that since we are using the "one-step" mode of the SUNDIALS
// solvers, they will, generally, step over the final time and will not
// explicitly perform the interpolation to t_final as they do in the
// "normal" step mode.
ode_solver->Step(u, t, dt_real);
last_step = (t >= t_final - 1e-8*dt);
if (last_step || (ti % vis_steps) == 0)
{
cout << "step " << ti << ", t = " << t << endl;
if (CVODESolver* cvode = dynamic_cast<CVODESolver*>(ode_solver.get()))
{
cvode->PrintInfo();
}
else if (ARKStepSolver* arkode = dynamic_cast<ARKStepSolver*>(ode_solver.get()))
{
arkode->PrintInfo();
}
u_gf.SetFromTrueDofs(u);
if (visualization)
{
sout << "solution\n" << *mesh << u_gf << flush;
}
if (visit)
{
visit_dc.SetCycle(ti);
visit_dc.SetTime(t);
visit_dc.Save();
}
}
oper.SetConductionTensor(u);
}
tic_toc.Stop();
cout << "Done, " << tic_toc.RealTime() << "s." << endl;
// 9. Save the final solution. This output can be viewed later using GLVis:
// "glvis -m ex16.mesh -g ex16-final.gf".
u_gf.Save("ex16-final.gf", precision);
return 0;
}
ConductionOperator::ConductionOperator(FiniteElementSpace &fes,
const real_t alpha, const real_t kappa,
const Vector &u,
const Type &ode_expression_type)
: TimeDependentOperator(fes.GetTrueVSize(), 0.0, ode_expression_type),
fespace(fes), M(&fespace), alpha(alpha), kappa(kappa), z(height)
{
// specify a relative tolerance for all solves with MFEM integrators
const real_t rel_tol = 1e-8;
M.AddDomainIntegrator(new MassIntegrator());
M.Assemble();
M.FormSystemMatrix(ess_tdof_list, Mmat);
M_solver.iterative_mode = false;
M_solver.SetRelTol(rel_tol); // will be overwritten with SUNDIALS integrators
M_solver.SetAbsTol(0.0);
M_solver.SetMaxIter(50);
M_solver.SetPrintLevel(0);
M_solver.SetPreconditioner(M_prec);
M_solver.SetOperator(Mmat);
T_solver.iterative_mode = false;
T_solver.SetRelTol(rel_tol); // will be overwritten with SUNDIALS integrators
T_solver.SetAbsTol(0.0);
T_solver.SetMaxIter(100);
T_solver.SetPrintLevel(0);
T_solver.SetPreconditioner(T_prec);
SetConductionTensor(u);
}
void ConductionOperator::SetConductionTensor(const Vector &u)
{
// Compute K(u_n).
GridFunction u_alpha_gf(&fespace);
u_alpha_gf.SetFromTrueDofs(u);
for (int i = 0; i < u_alpha_gf.Size(); i++)
{
u_alpha_gf(i) = kappa + alpha*u_alpha_gf(i);
}
GridFunctionCoefficient u_coeff(&u_alpha_gf);
K = std::make_unique<BilinearForm>(&fespace);
K->AddDomainIntegrator(new DiffusionIntegrator(u_coeff));
K->Assemble();
K->FormSystemMatrix(ess_tdof_list, Kmat);
}
void ConductionOperator::ExplicitMult(const Vector &u, Vector &v) const
{
// Compute - K(u_n) u.
Kmat.Mult(u, v);
v.Neg();
}
void ConductionOperator::Mult(const Vector &u, Vector &k) const
{
// Compute - inv(M) K(u_n) u.
ExplicitMult(u, z);
M_solver.Mult(z, k);
}
void ConductionOperator::ImplicitSolve(const real_t gam, const Vector &u,
Vector &k)
{
// Solve for k in M k = - K(u_n) [u + gam*k].
ExplicitMult(u, z);
T = std::unique_ptr<SparseMatrix>(Add(1.0, Mmat, gam, Kmat));
T_solver.SetOperator(*T);
T_solver.Mult(z, k);
}
int ConductionOperator::SUNImplicitSetup(const Vector &u, const Vector &fu,
int jok, int *jcur, real_t gam)
{
// Compute T = M + gamma K(u_n).
T = std::unique_ptr<SparseMatrix>(Add(1.0, Mmat, gam, Kmat));
T_solver.SetOperator(*T);
*jcur = SUNTRUE; // this should eventually only be set true if K(u) is used
return SUN_SUCCESS;
}
int ConductionOperator::SUNImplicitSolve(const Vector &r, Vector &dk,
real_t tol)
{
// Solve the system [M + gamma K(u_n)] dk = - K(u_n) u - M k.
// What value r is providing depends on the ODE expression form:
// EXPLICIT form: r = -inv(M) K(u_n) u - k
// IMPLICIT form: r = -K(u_n) u - M k
T_solver.SetRelTol(tol);
if (isExplicit())
{
Mmat.Mult(r, z);
T_solver.Mult(z, dk);
}
else
{
T_solver.Mult(r, dk);
}
if (T_solver.GetConverged())
{
return SUN_SUCCESS;
}
else
{
return SUNLS_CONV_FAIL;
}
}
int ConductionOperator::SUNMassSetup()
{
// Do nothing b/c mass solver was setup in constructor.
return SUN_SUCCESS;
}
int ConductionOperator::SUNMassSolve(const Vector &b, Vector &x, real_t tol)
{
// Solve the system M x = b.
M_solver.SetRelTol(tol);
M_solver.Mult(b, x);
if (M_solver.GetConverged())
{
return SUN_SUCCESS;
}
else
{
return SUNLS_CONV_FAIL;
}
}
int ConductionOperator::SUNMassMult(const Vector &x, Vector &v)
{
// Compute M x.
Mmat.Mult(x, v);
return SUN_SUCCESS;
}