double L2ZZErrorEstimator(BilinearFormIntegrator &flux_integrator,
const ParGridFunction &x,
ParFiniteElementSpace &smooth_flux_fes,
ParFiniteElementSpace &flux_fes,
Vector &errors,
int norm_p, double solver_tol, int solver_max_it)
{
// Compute fluxes in discontinuous space
GridFunction flux(&flux_fes);
flux = 0.0;
ParFiniteElementSpace *xfes = x.ParFESpace();
Array<int> xdofs, fdofs;
Vector el_x, el_f;
for (int i = 0; i < xfes->GetNE(); i++)
{
xfes->GetElementVDofs(i, xdofs);
x.GetSubVector(xdofs, el_x);
ElementTransformation *Transf = xfes->GetElementTransformation(i);
flux_integrator.ComputeElementFlux(*xfes->GetFE(i), *Transf, el_x,
*flux_fes.GetFE(i), el_f, false);
flux_fes.GetElementVDofs(i, fdofs);
flux.AddElementVector(fdofs, el_f);
}
// Assemble the linear system for L2 projection into the "smooth" space
ParBilinearForm *a = new ParBilinearForm(&smooth_flux_fes);
ParLinearForm *b = new ParLinearForm(&smooth_flux_fes);
VectorGridFunctionCoefficient f(&flux);
if (xfes->GetNE())
{
if (smooth_flux_fes.GetFE(0)->GetRangeType() == FiniteElement::SCALAR)
{
VectorMassIntegrator *vmass = new VectorMassIntegrator;
vmass->SetVDim(smooth_flux_fes.GetVDim());
a->AddDomainIntegrator(vmass);
b->AddDomainIntegrator(new VectorDomainLFIntegrator(f));
}
else
{
a->AddDomainIntegrator(new VectorFEMassIntegrator);
b->AddDomainIntegrator(new VectorFEDomainLFIntegrator(f));
}
}
b->Assemble();
a->Assemble();
a->Finalize();
// The destination of the projected discontinuous flux
ParGridFunction smooth_flux(&smooth_flux_fes);
smooth_flux = 0.0;
HypreParMatrix* A = a->ParallelAssemble();
HypreParVector* B = b->ParallelAssemble();
HypreParVector* X = smooth_flux.ParallelProject();
delete a;
delete b;
// Define and apply a parallel PCG solver for AX=B with the BoomerAMG
// preconditioner from hypre.
HypreBoomerAMG *amg = new HypreBoomerAMG(*A);
amg->SetPrintLevel(0);
HyprePCG *pcg = new HyprePCG(*A);
pcg->SetTol(solver_tol);
pcg->SetMaxIter(solver_max_it);
pcg->SetPrintLevel(0);
pcg->SetPreconditioner(*amg);
pcg->Mult(*B, *X);
// Extract the parallel grid function corresponding to the finite element
// approximation X. This is the local solution on each processor.
smooth_flux = *X;
delete A;
delete B;
delete X;
delete amg;
delete pcg;
// Proceed through the elements one by one, and find the Lp norm differences
// between the flux as computed per element and the flux projected onto the
// smooth_flux_fes space.
double total_error = 0.0;
errors.SetSize(xfes->GetNE());
for (int i = 0; i < xfes->GetNE(); i++)
{
errors(i) = ComputeElementLpDistance(norm_p, i, smooth_flux, flux);
total_error += pow(errors(i), norm_p);
}
double glob_error;
MPI_Allreduce(&total_error, &glob_error, 1, MPI_DOUBLE, MPI_SUM,
xfes->GetComm());
return pow(glob_error, 1.0/norm_p);
}
int main(int argc, char *argv[])
{
// 0. Initialize MPI.
int num_procs, myid;
MPI_Init(&argc, &argv);
MPI_Comm_size(MPI_COMM_WORLD, &num_procs);
MPI_Comm_rank(MPI_COMM_WORLD, &myid);
// 1. Parse command-line options.
const char *mesh_file = "../data/beam-tri.mesh";
int serial_ref_levels = 0;
int order = 1;
bool static_cond = false;
bool visualization = 1;
OptionsParser args(argc, argv);
args.AddOption(&mesh_file, "-m", "--mesh",
"Mesh file to use.");
args.AddOption(&serial_ref_levels, "-rs", "--refine-serial",
"Number of uniform serial refinements (before parallel"
" partitioning)");
args.AddOption(&order, "-o", "--order",
"Finite element order (polynomial degree).");
args.AddOption(&static_cond, "-sc", "--static-condensation", "-no-sc",
"--no-static-condensation", "Enable static condensation.");
args.AddOption(&visualization, "-vis", "--visualization", "-no-vis",
"--no-visualization",
"Enable or disable GLVis visualization.");
args.Parse();
if (!args.Good())
{
if (myid == 0)
{
args.PrintUsage(cout);
}
MPI_Finalize();
return 1;
}
if (myid == 0)
{
args.PrintOptions(cout);
}
// 2. Read the mesh from the given mesh file. We can handle triangular,
// quadrilateral, tetrahedral, and hexahedral meshes with the same code.
Mesh mesh(mesh_file, 1, 1);
int dim = mesh.Dimension();
MFEM_VERIFY(mesh.SpaceDimension() == dim, "invalid mesh");
if (mesh.attributes.Max() < 2 || mesh.bdr_attributes.Max() < 2)
{
cerr << "\nInput mesh should have at least two materials and "
<< "two boundary attributes! (See schematic in ex2.cpp)\n"
<< endl;
MPI_Finalize();
return 3;
}
// 3. Refine the mesh before parallel partitioning. Since a NURBS mesh can
// currently only be refined uniformly, we need to convert it to a
// piecewise-polynomial curved mesh. First we refine the NURBS mesh a bit
// more and then project the curvature to quadratic Nodes.
if (mesh.NURBSext && serial_ref_levels == 0)
{
serial_ref_levels = 2;
}
for (int i = 0; i < serial_ref_levels; i++)
{
mesh.UniformRefinement();
}
if (mesh.NURBSext)
{
mesh.SetCurvature(2);
}
mesh.EnsureNCMesh();
ParMesh pmesh(MPI_COMM_WORLD, mesh);
mesh.Clear();
// 4. Define a finite element space on the mesh. The polynomial order is
// one (linear) by default, but this can be changed on the command line.
H1_FECollection fec(order, dim);
ParFiniteElementSpace fespace(&pmesh, &fec, dim);
// 5. As in Example 2, we set up the linear form b(.) which corresponds to
// the right-hand side of the FEM linear system. In this case, b_i equals
// the boundary integral of f*phi_i where f represents a "pull down"
// force on the Neumann part of the boundary and phi_i are the basis
// functions in the finite element fespace. The force is defined by the
// VectorArrayCoefficient object f, which is a vector of Coefficient
// objects. The fact that f is non-zero on boundary attribute 2 is
// indicated by the use of piece-wise constants coefficient for its last
// component. We don't assemble the discrete problem yet, this will be
// done in the main loop.
VectorArrayCoefficient f(dim);
for (int i = 0; i < dim-1; i++)
{
f.Set(i, new ConstantCoefficient(0.0));
}
{
Vector pull_force(pmesh.bdr_attributes.Max());
pull_force = 0.0;
pull_force(1) = -1.0e-2;
f.Set(dim-1, new PWConstCoefficient(pull_force));
}
ParLinearForm b(&fespace);
b.AddDomainIntegrator(new VectorBoundaryLFIntegrator(f));
// 6. Set up the bilinear form a(.,.) on the finite element space
// corresponding to the linear elasticity integrator with piece-wise
// constants coefficient lambda and mu.
Vector lambda(pmesh.attributes.Max());
lambda = 1.0;
lambda(0) = lambda(1)*50;
PWConstCoefficient lambda_func(lambda);
Vector mu(pmesh.attributes.Max());
mu = 1.0;
mu(0) = mu(1)*50;
PWConstCoefficient mu_func(mu);
ParBilinearForm a(&fespace);
BilinearFormIntegrator *integ =
new ElasticityIntegrator(lambda_func,mu_func);
a.AddDomainIntegrator(integ);
if (static_cond) { a.EnableStaticCondensation(); }
// 7. The solution vector x and the associated finite element grid function
// will be maintained over the AMR iterations. We initialize it to zero.
Vector zero_vec(dim);
zero_vec = 0.0;
VectorConstantCoefficient zero_vec_coeff(zero_vec);
ParGridFunction x(&fespace);
x = 0.0;
// 8. Determine the list of true (i.e. conforming) essential boundary dofs.
// In this example, the boundary conditions are defined by marking only
// boundary attribute 1 from the mesh as essential and converting it to a
// list of true dofs. The conversion to true dofs will be done in the
// main loop.
Array<int> ess_bdr(pmesh.bdr_attributes.Max());
ess_bdr = 0;
ess_bdr[0] = 1;
// 9. GLVis visualization.
char vishost[] = "localhost";
int visport = 19916;
socketstream sol_sock;
// 10. Set up an error estimator. Here we use the Zienkiewicz-Zhu estimator
// that uses the ComputeElementFlux method of the ElasticityIntegrator to
// recover a smoothed flux (stress) that is subtracted from the element
// flux to get an error indicator. We need to supply the space for the
// smoothed flux: an (H1)^tdim (i.e., vector-valued) space is used here.
// Here, tdim represents the number of components for a symmetric (dim x
// dim) tensor.
const int tdim = dim*(dim+1)/2;
L2_FECollection flux_fec(order, dim);
ParFiniteElementSpace flux_fespace(&pmesh, &flux_fec, tdim);
ParFiniteElementSpace smooth_flux_fespace(&pmesh, &fec, tdim);
L2ZienkiewiczZhuEstimator estimator(*integ, x, flux_fespace,
smooth_flux_fespace);
// 11. A refiner selects and refines elements based on a refinement strategy.
// The strategy here is to refine elements with errors larger than a
// fraction of the maximum element error. Other strategies are possible.
// The refiner will call the given error estimator.
ThresholdRefiner refiner(estimator);
refiner.SetTotalErrorFraction(0.7);
// 12. The main AMR loop. In each iteration we solve the problem on the
// current mesh, visualize the solution, and refine the mesh.
const int max_dofs = 50000;
const int max_amr_itr = 20;
for (int it = 0; it <= max_amr_itr; it++)
{
HYPRE_Int global_dofs = fespace.GlobalTrueVSize();
if (myid == 0)
{
cout << "\nAMR iteration " << it << endl;
cout << "Number of unknowns: " << global_dofs << endl;
}
// 13. Assemble the stiffness matrix and the right-hand side.
a.Assemble();
b.Assemble();
// 14. Set Dirichlet boundary values in the GridFunction x.
// Determine the list of Dirichlet true DOFs in the linear system.
Array<int> ess_tdof_list;
x.ProjectBdrCoefficient(zero_vec_coeff, ess_bdr);
fespace.GetEssentialTrueDofs(ess_bdr, ess_tdof_list);
// 15. Create the linear system: eliminate boundary conditions, constrain
// hanging nodes and possibly apply other transformations. The system
// will be solved for true (unconstrained) DOFs only.
HypreParMatrix A;
Vector B, X;
const int copy_interior = 1;
a.FormLinearSystem(ess_tdof_list, x, b, A, X, B, copy_interior);
// 16. Define and apply a parallel PCG solver for AX=B with the BoomerAMG
// preconditioner from hypre.
HypreBoomerAMG amg;
amg.SetPrintLevel(0);
// amg.SetSystemsOptions(dim); // optional
CGSolver pcg(A.GetComm());
pcg.SetPreconditioner(amg);
pcg.SetOperator(A);
pcg.SetRelTol(1e-6);
pcg.SetMaxIter(500);
pcg.SetPrintLevel(3); // print the first and the last iterations only
pcg.Mult(B, X);
// 17. After solving the linear system, reconstruct the solution as a
// finite element GridFunction. Constrained nodes are interpolated
// from true DOFs (it may therefore happen that x.Size() >= X.Size()).
a.RecoverFEMSolution(X, b, x);
// 18. Send solution by socket to the GLVis server.
if (visualization && it == 0)
{
sol_sock.open(vishost, visport);
sol_sock.precision(8);
}
if (visualization && sol_sock.good())
{
GridFunction nodes(&fespace), *nodes_p = &nodes;
pmesh.GetNodes(nodes);
nodes += x;
int own_nodes = 0;
pmesh.SwapNodes(nodes_p, own_nodes);
x.Neg(); // visualize the backward displacement
sol_sock << "parallel " << num_procs << ' ' << myid << '\n';
sol_sock << "solution\n" << pmesh << x << flush;
x.Neg();
pmesh.SwapNodes(nodes_p, own_nodes);
if (it == 0)
{
sol_sock << "keys '" << ((dim == 2) ? "Rjl" : "") << "m'" << endl;
}
sol_sock << "window_title 'AMR iteration: " << it << "'\n"
<< "pause" << endl;
if (myid == 0)
{
cout << "Visualization paused. "
"Press <space> in the GLVis window to continue." << endl;
}
}
if (global_dofs > max_dofs)
{
if (myid == 0)
{
cout << "Reached the maximum number of dofs. Stop." << endl;
}
break;
}
// 19. Call the refiner to modify the mesh. The refiner calls the error
// estimator to obtain element errors, then it selects elements to be
// refined and finally it modifies the mesh. The Stop() method can be
// used to determine if a stopping criterion was met.
refiner.Apply(pmesh);
if (refiner.Stop())
{
if (myid == 0)
{
cout << "Stopping criterion satisfied. Stop." << endl;
}
break;
}
// 20. Update the space to reflect the new state of the mesh. Also,
// interpolate the solution x so that it lies in the new space but
// represents the same function. This saves solver iterations later
// since we'll have a good initial guess of x in the next step.
// Internally, FiniteElementSpace::Update() calculates an
// interpolation matrix which is then used by GridFunction::Update().
fespace.Update();
x.Update();
// 21. Load balance the mesh, and update the space and solution. Currently
// available only for nonconforming meshes.
if (pmesh.Nonconforming())
{
pmesh.Rebalance();
// Update the space and the GridFunction. This time the update matrix
// redistributes the GridFunction among the processors.
fespace.Update();
x.Update();
}
// 22. Inform also the bilinear and linear forms that the space has
// changed.
a.Update();
b.Update();
}
{
ostringstream mref_name, mesh_name, sol_name;
mref_name << "ex22p_reference_mesh." << setfill('0') << setw(6) << myid;
mesh_name << "ex22p_deformed_mesh." << setfill('0') << setw(6) << myid;
sol_name << "ex22p_displacement." << setfill('0') << setw(6) << myid;
ofstream mesh_ref_out(mref_name.str().c_str());
mesh_ref_out.precision(16);
pmesh.Print(mesh_ref_out);
ofstream mesh_out(mesh_name.str().c_str());
mesh_out.precision(16);
GridFunction nodes(&fespace), *nodes_p = &nodes;
pmesh.GetNodes(nodes);
nodes += x;
int own_nodes = 0;
pmesh.SwapNodes(nodes_p, own_nodes);
pmesh.Print(mesh_out);
pmesh.SwapNodes(nodes_p, own_nodes);
ofstream x_out(sol_name.str().c_str());
x_out.precision(16);
x.Save(x_out);
}
MPI_Finalize();
return 0;
}
int main(int argc, char *argv[])
{
// 1. Initialize MPI.
int num_procs, myid;
MPI_Init(&argc, &argv);
MPI_Comm_size(MPI_COMM_WORLD, &num_procs);
MPI_Comm_rank(MPI_COMM_WORLD, &myid);
// 2. Parse command-line options.
const char *mesh_file = "../data/beam-tri.mesh";
int order = 1;
int nev = 5;
bool visualization = 1;
bool amg_elast = 0;
OptionsParser args(argc, argv);
args.AddOption(&mesh_file, "-m", "--mesh",
"Mesh file to use.");
args.AddOption(&order, "-o", "--order",
"Finite element order (polynomial degree).");
args.AddOption(&nev, "-n", "--num-eigs",
"Number of desired eigenmodes.");
args.AddOption(&amg_elast, "-elast", "--amg-for-elasticity", "-sys",
"--amg-for-systems",
"Use the special AMG elasticity solver (GM/LN approaches), "
"or standard AMG for systems (unknown approach).");
args.AddOption(&visualization, "-vis", "--visualization", "-no-vis",
"--no-visualization",
"Enable or disable GLVis visualization.");
args.Parse();
if (!args.Good())
{
if (myid == 0)
{
args.PrintUsage(cout);
}
MPI_Finalize();
return 1;
}
if (myid == 0)
{
args.PrintOptions(cout);
}
// 3. Read the (serial) mesh from the given mesh file on all processors. We
// can handle triangular, quadrilateral, tetrahedral, hexahedral, surface
// and volume meshes with the same code.
Mesh *mesh = new Mesh(mesh_file, 1, 1);
int dim = mesh->Dimension();
if (mesh->attributes.Max() < 2)
{
if (myid == 0)
cerr << "\nInput mesh should have at least two materials!"
<< " (See schematic in ex12p.cpp)\n"
<< endl;
MPI_Finalize();
return 3;
}
// 4. Select the order of the finite element discretization space. For NURBS
// meshes, we increase the order by degree elevation.
if (mesh->NURBSext && order > mesh->NURBSext->GetOrder())
{
mesh->DegreeElevate(order - mesh->NURBSext->GetOrder());
}
// 5. Refine the serial mesh on all processors to increase the resolution. In
// this example we do 'ref_levels' of uniform refinement. We choose
// 'ref_levels' to be the largest number that gives a final mesh with no
// more than 1,000 elements.
{
int ref_levels =
(int)floor(log(1000./mesh->GetNE())/log(2.)/dim);
for (int l = 0; l < ref_levels; l++)
{
mesh->UniformRefinement();
}
}
// 6. Define a parallel mesh by a partitioning of the serial mesh. Refine
// this mesh further in parallel to increase the resolution. Once the
// parallel mesh is defined, the serial mesh can be deleted.
ParMesh *pmesh = new ParMesh(MPI_COMM_WORLD, *mesh);
delete mesh;
{
int par_ref_levels = 1;
for (int l = 0; l < par_ref_levels; l++)
{
pmesh->UniformRefinement();
}
}
// 7. Define a parallel finite element space on the parallel mesh. Here we
// use vector finite elements, i.e. dim copies of a scalar finite element
// space. We use the ordering by vector dimension (the last argument of
// the FiniteElementSpace constructor) which is expected in the systems
// version of BoomerAMG preconditioner. For NURBS meshes, we use the
// (degree elevated) NURBS space associated with the mesh nodes.
FiniteElementCollection *fec;
ParFiniteElementSpace *fespace;
const bool use_nodal_fespace = pmesh->NURBSext && !amg_elast;
if (use_nodal_fespace)
{
fec = NULL;
fespace = (ParFiniteElementSpace *)pmesh->GetNodes()->FESpace();
}
else
{
fec = new H1_FECollection(order, dim);
fespace = new ParFiniteElementSpace(pmesh, fec, dim, Ordering::byVDIM);
}
HYPRE_Int size = fespace->GlobalTrueVSize();
if (myid == 0)
{
cout << "Number of unknowns: " << size << endl
<< "Assembling: " << flush;
}
// 8. Set up the parallel bilinear forms a(.,.) and m(.,.) on the finite
// element space corresponding to the linear elasticity integrator with
// piece-wise constants coefficient lambda and mu, a simple mass matrix
// needed on the right hand side of the generalized eigenvalue problem
// below. The boundary conditions are implemented by marking only boundary
// attribute 1 as essential. We use special values on the diagonal to
// shift the Dirichlet eigenvalues out of the computational range. After
// serial/parallel assembly we extract the corresponding parallel matrices
// A and M.
Vector lambda(pmesh->attributes.Max());
lambda = 1.0;
lambda(0) = lambda(1)*50;
PWConstCoefficient lambda_func(lambda);
Vector mu(pmesh->attributes.Max());
mu = 1.0;
mu(0) = mu(1)*50;
PWConstCoefficient mu_func(mu);
Array<int> ess_bdr(pmesh->bdr_attributes.Max());
ess_bdr = 0;
ess_bdr[0] = 1;
ParBilinearForm *a = new ParBilinearForm(fespace);
a->AddDomainIntegrator(new ElasticityIntegrator(lambda_func, mu_func));
if (myid == 0)
{
cout << "matrix ... " << flush;
}
a->Assemble();
a->EliminateEssentialBCDiag(ess_bdr, 1.0);
a->Finalize();
ParBilinearForm *m = new ParBilinearForm(fespace);
m->AddDomainIntegrator(new VectorMassIntegrator());
m->Assemble();
// shift the eigenvalue corresponding to eliminated dofs to a large value
m->EliminateEssentialBCDiag(ess_bdr, numeric_limits<double>::min());
m->Finalize();
if (myid == 0)
{
cout << "done." << endl;
}
HypreParMatrix *A = a->ParallelAssemble();
HypreParMatrix *M = m->ParallelAssemble();
delete a;
delete m;
// 9. Define and configure the LOBPCG eigensolver and the BoomerAMG
// preconditioner for A to be used within the solver. Set the matrices
// which define the generalized eigenproblem A x = lambda M x.
HypreBoomerAMG * amg = new HypreBoomerAMG(*A);
amg->SetPrintLevel(0);
if (amg_elast)
{
amg->SetElasticityOptions(fespace);
}
else
{
amg->SetSystemsOptions(dim);
}
HypreLOBPCG * lobpcg = new HypreLOBPCG(MPI_COMM_WORLD);
lobpcg->SetNumModes(nev);
lobpcg->SetPreconditioner(*amg);
lobpcg->SetMaxIter(100);
lobpcg->SetTol(1e-8);
lobpcg->SetPrecondUsageMode(1);
lobpcg->SetPrintLevel(1);
lobpcg->SetMassMatrix(*M);
lobpcg->SetOperator(*A);
// 10. Compute the eigenmodes and extract the array of eigenvalues. Define a
// parallel grid function to represent each of the eigenmodes returned by
// the solver.
Array<double> eigenvalues;
lobpcg->Solve();
lobpcg->GetEigenvalues(eigenvalues);
ParGridFunction x(fespace);
// 11. For non-NURBS meshes, make the mesh curved based on the finite element
// space. This means that we define the mesh elements through a fespace
// based transformation of the reference element. This allows us to save
// the displaced mesh as a curved mesh when using high-order finite
// element displacement field. We assume that the initial mesh (read from
// the file) is not higher order curved mesh compared to the chosen FE
// space.
if (!use_nodal_fespace)
{
pmesh->SetNodalFESpace(fespace);
}
// 12. Save the refined mesh and the modes in parallel. This output can be
// viewed later using GLVis: "glvis -np <np> -m mesh -g mode".
{
ostringstream mesh_name, mode_name;
mesh_name << "mesh." << setfill('0') << setw(6) << myid;
ofstream mesh_ofs(mesh_name.str().c_str());
mesh_ofs.precision(8);
pmesh->Print(mesh_ofs);
for (int i=0; i<nev; i++)
{
// convert eigenvector from HypreParVector to ParGridFunction
x = lobpcg->GetEigenvector(i);
mode_name << "mode_" << setfill('0') << setw(2) << i << "."
<< setfill('0') << setw(6) << myid;
ofstream mode_ofs(mode_name.str().c_str());
mode_ofs.precision(8);
x.Save(mode_ofs);
mode_name.str("");
}
}
// 13. Send the above data by socket to a GLVis server. Use the "n" and "b"
// keys in GLVis to visualize the displacements.
if (visualization)
{
char vishost[] = "localhost";
int visport = 19916;
socketstream mode_sock(vishost, visport);
for (int i=0; i<nev; i++)
{
if ( myid == 0 )
{
cout << "Eigenmode " << i+1 << '/' << nev
<< ", Lambda = " << eigenvalues[i] << endl;
}
// convert eigenvector from HypreParVector to ParGridFunction
x = lobpcg->GetEigenvector(i);
mode_sock << "parallel " << num_procs << " " << myid << "\n"
<< "solution\n" << *pmesh << x << flush
<< "window_title 'Eigenmode " << i+1 << '/' << nev
<< ", Lambda = " << eigenvalues[i] << "'" << endl;
char c;
if (myid == 0)
{
cout << "press (q)uit or (c)ontinue --> " << flush;
cin >> c;
}
MPI_Bcast(&c, 1, MPI_CHAR, 0, MPI_COMM_WORLD);
if (c != 'c')
{
break;
}
}
mode_sock.close();
}