MFEM v4.7.0 Finite element discretization library
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ex1p.cpp
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1// MFEM Example 1 - Parallel Version
2// AmgX Modification
3//
4// Compile with: make ex1p
5//
6// AmgX sample runs:
7// mpirun -np 4 ex1p
8// mpirun -np 4 ex1p -d cuda
9// mpirun -np 10 ex1p --amgx-file amg_pcg.json --amgx-mpi-teams
10// mpirun -np 4 ex1p --amgx-file amg_pcg.json
11//
12// Description: This example code demonstrates the use of MFEM to define a
13// simple finite element discretization of the Laplace problem
14// -Delta u = 1 with homogeneous Dirichlet boundary conditions.
15// Specifically, we discretize using a FE space of the specified
16// order, or if order < 1 using an isoparametric/isogeometric
18// NURBS mesh, etc.)
19//
20// The example highlights the use of mesh refinement, finite
21// element grid functions, as well as linear and bilinear forms
22// corresponding to the left-hand side and right-hand side of the
23// discrete linear system. We also cover the explicit elimination
24// of essential boundary conditions, static condensation, and the
25// optional connection to the GLVis tool for visualization.
26
27#include "mfem.hpp"
28#include <fstream>
29#include <iostream>
30
31using namespace std;
32using namespace mfem;
33
34#ifndef MFEM_USE_AMGX
35#error This example requires that MFEM is built with MFEM_USE_AMGX=YES
36#endif
37
38int main(int argc, char *argv[])
39{
40 // 1. Initialize MPI and HYPRE.
41 Mpi::Init(argc, argv);
42 int num_procs = Mpi::WorldSize();
43 int myid = Mpi::WorldRank();
45
46 // 2. Parse command-line options.
47 const char *mesh_file = "../../data/star.mesh";
48 int order = 1;
49 bool static_cond = false;
50 bool pa = false;
51 const char *device_config = "cpu";
52 bool visualization = true;
53 bool amgx_lib = true;
54 bool amgx_mpi_teams = false;
55 const char* amgx_json_file = ""; // JSON file for AmgX
56 int ndevices = 1;
57
58 OptionsParser args(argc, argv);
60 "Mesh file to use.");
62 "Finite element order (polynomial degree) or -1 for"
63 " isoparametric space.");
65 "--no-static-condensation", "Enable static condensation.");
67 "--no-partial-assembly", "Enable Partial Assembly.");
69 "--no-amgx-lib", "Use AmgX in example.");
71 "AMGX solver config file (overrides --amgx-solver, --amgx-verbose)");
73 "--amgx-mpi-gpu-exclusive", "--amgx-mpi-gpu-exclusive",
74 "Create MPI teams when using AmgX to load balance between ranks and GPUs.");
76 "Device configuration string, see Device::Configure().");
78 "--no-visualization",
79 "Enable or disable GLVis visualization.");
81 "Number of GPU devices per node (Only used if amgx_mpi_teams is true).");
82
83 args.Parse();
84 if (!args.Good())
85 {
86 if (myid == 0)
87 {
88 args.PrintUsage(cout);
89 }
90 return 1;
91 }
92 if (myid == 0)
93 {
94 args.PrintOptions(cout);
95 }
96
97 // 3. Enable hardware devices such as GPUs, and programming models such as
98 // CUDA, OCCA, RAJA and OpenMP based on command line options.
99 Device device(device_config);
100 if (myid == 0) { device.Print(); }
101
102 // 4. Read the (serial) mesh from the given mesh file on all processors. We
103 // can handle triangular, quadrilateral, tetrahedral, hexahedral, surface
104 // and volume meshes with the same code.
105 Mesh mesh(mesh_file, 1, 1);
106 int dim = mesh.Dimension();
107
108 // 5. Refine the serial mesh on all processors to increase the resolution. In
109 // this example we do 'ref_levels' of uniform refinement. We choose
110 // 'ref_levels' to be the largest number that gives a final mesh with no
111 // more than 10,000 elements.
112 {
113 int ref_levels =
114 (int)floor(log(10000./mesh.GetNE())/log(2.)/dim);
115 for (int l = 0; l < ref_levels; l++)
116 {
117 mesh.UniformRefinement();
118 }
119 }
120
121 // 6. Define a parallel mesh by a partitioning of the serial mesh. Refine
122 // this mesh further in parallel to increase the resolution. Once the
123 // parallel mesh is defined, the serial mesh can be deleted.
124 ParMesh pmesh(MPI_COMM_WORLD, mesh);
125 mesh.Clear();
126 {
127 int par_ref_levels = 2;
128 for (int l = 0; l < par_ref_levels; l++)
129 {
130 pmesh.UniformRefinement();
131 }
132 }
133
134 // 7. Define a parallel finite element space on the parallel mesh. Here we
135 // use continuous Lagrange finite elements of the specified order. If
136 // order < 1, we instead use an isoparametric/isogeometric space.
138 bool delete_fec;
139 if (order > 0)
140 {
141 fec = new H1_FECollection(order, dim);
142 delete_fec = true;
143 }
144 else if (pmesh.GetNodes())
145 {
146 fec = pmesh.GetNodes()->OwnFEC();
147 delete_fec = false;
148 if (myid == 0)
149 {
150 cout << "Using isoparametric FEs: " << fec->Name() << endl;
151 }
152 }
153 else
154 {
155 fec = new H1_FECollection(order = 1, dim);
156 delete_fec = true;
157 }
158 ParFiniteElementSpace fespace(&pmesh, fec);
159 HYPRE_BigInt size = fespace.GlobalTrueVSize();
160 if (myid == 0)
161 {
162 cout << "Number of finite element unknowns: " << size << endl;
163 }
164
165 // 8. Determine the list of true (i.e. parallel conforming) essential
166 // boundary dofs. In this example, the boundary conditions are defined
167 // by marking all the boundary attributes from the mesh as essential
168 // (Dirichlet) and converting them to a list of true dofs.
169 Array<int> ess_tdof_list;
170 if (pmesh.bdr_attributes.Size())
171 {
172 Array<int> ess_bdr(pmesh.bdr_attributes.Max());
173 ess_bdr = 1;
174 fespace.GetEssentialTrueDofs(ess_bdr, ess_tdof_list);
175 }
176
177 // 9. Set up the parallel linear form b(.) which corresponds to the
178 // right-hand side of the FEM linear system, which in this case is
179 // (1,phi_i) where phi_i are the basis functions in fespace.
180 ParLinearForm b(&fespace);
181 ConstantCoefficient one(1.0);
183 b.Assemble();
184
185 // 10. Define the solution vector x as a parallel finite element grid function
186 // corresponding to fespace. Initialize x with initial guess of zero,
187 // which satisfies the boundary conditions.
188 ParGridFunction x(&fespace);
189 x = 0.0;
190
191 // 11. Set up the parallel bilinear form a(.,.) on the finite element space
192 // corresponding to the Laplacian operator -Delta, by adding the Diffusion
193 // domain integrator.
194 ParBilinearForm a(&fespace);
195 if (pa) { a.SetAssemblyLevel(AssemblyLevel::PARTIAL); }
197
198 // 12. Assemble the parallel bilinear form and the corresponding linear
199 // system, applying any necessary transformations such as: parallel
200 // assembly, eliminating boundary conditions, applying conforming
201 // constraints for non-conforming AMR, static condensation, etc.
202 if (static_cond) { a.EnableStaticCondensation(); }
203 a.Assemble();
204
205 OperatorPtr A;
206 Vector B, X;
207 a.FormLinearSystem(ess_tdof_list, x, b, A, X, B);
208
209 // 13. Solve the linear system A X = B.
210 // * With full assembly, use the BoomerAMG preconditioner from hypre.
211 // * If AmgX is available solve using amg preconditioner.
212 // * With partial assembly, use Jacobi smoothing, for now.
213 Solver *prec = NULL;
214 if (pa)
215 {
216 if (UsesTensorBasis(fespace))
217 {
218 prec = new OperatorJacobiSmoother(a, ess_tdof_list);
219 }
220
221 CGSolver cg(MPI_COMM_WORLD);
222 cg.SetRelTol(1e-12);
223 cg.SetMaxIter(2000);
224 cg.SetPrintLevel(1);
225 if (prec) { cg.SetPreconditioner(*prec); }
226 cg.SetOperator(*A);
227 cg.Mult(B, X);
228 delete prec;
229 }
230 else if (amgx_lib && strcmp(amgx_json_file,"") == 0)
231 {
232 MFEM_VERIFY(!amgx_mpi_teams,
233 "Please add JSON file to try AmgX with MPI teams mode");
234
235 bool amgx_verbose = false;
236 prec = new AmgXSolver(MPI_COMM_WORLD, AmgXSolver::PRECONDITIONER,
237 amgx_verbose);
238
239 CGSolver cg(MPI_COMM_WORLD);
240 cg.SetRelTol(1e-12);
241 cg.SetMaxIter(2000);
242 cg.SetPrintLevel(1);
243 if (prec) { cg.SetPreconditioner(*prec); }
244 cg.SetOperator(*A);
245 cg.Mult(B, X);
246 delete prec;
247
248 }
249 else if (amgx_lib && strcmp(amgx_json_file,"") != 0)
250 {
251 AmgXSolver amgx;
253
254 if (amgx_mpi_teams)
255 {
256 // Forms MPI teams to load balance between MPI ranks and GPUs
257 amgx.InitMPITeams(MPI_COMM_WORLD, ndevices);
258 }
259 else
260 {
261 // Assumes each MPI rank is paired with a GPU
262 amgx.InitExclusiveGPU(MPI_COMM_WORLD);
263 }
264
265 amgx.SetOperator(*A.As<HypreParMatrix>());
266 amgx.SetConvergenceCheck(true);
267 amgx.Mult(B, X);
268
269 // Release MPI communicators and resources created by AmgX
270 amgx.Finalize();
271 }
272 else
273 {
274 prec = new HypreBoomerAMG;
275
276 CGSolver cg(MPI_COMM_WORLD);
277 cg.SetRelTol(1e-12);
278 cg.SetMaxIter(2000);
279 cg.SetPrintLevel(1);
280 if (prec) { cg.SetPreconditioner(*prec); }
281 cg.SetOperator(*A);
282 cg.Mult(B, X);
283 delete prec;
284 }
285
286 // 14. Recover the parallel grid function corresponding to X. This is the
287 // local finite element solution on each processor.
288 a.RecoverFEMSolution(X, b, x);
289
290 // 15. Save the refined mesh and the solution in parallel. This output can
291 // be viewed later using GLVis: "glvis -np <np> -m mesh -g sol".
292 {
293 ostringstream mesh_name, sol_name;
294 mesh_name << "mesh." << setfill('0') << setw(6) << myid;
295 sol_name << "sol." << setfill('0') << setw(6) << myid;
296
297 ofstream mesh_ofs(mesh_name.str().c_str());
298 mesh_ofs.precision(8);
299 pmesh.Print(mesh_ofs);
300
301 ofstream sol_ofs(sol_name.str().c_str());
302 sol_ofs.precision(8);
303 x.Save(sol_ofs);
304 }
305
306 // 16. Send the solution by socket to a GLVis server.
307 if (visualization)
308 {
309 char vishost[] = "localhost";
310 int visport = 19916;
311 socketstream sol_sock(vishost, visport);
312 sol_sock << "parallel " << num_procs << " " << myid << "\n";
313 sol_sock.precision(8);
314 sol_sock << "solution\n" << pmesh << x << flush;
315 }
316
317 // 17. Free the used memory.
318 if (delete_fec)
319 {
320 delete fec;
321 }
322
323 return 0;
324}
MFEM wrapper for Nvidia's multigrid library, AmgX (github.com/NVIDIA/AMGX)
@ EXTERNAL
Configure will be read from a specified file.
void Finalize()
Close down the AmgX library and free up any MPI Comms set up for it.
virtual void SetOperator(const Operator &op)
Sets the Operator that is going to be solved via AmgX. Supports operators based on either an MFEM Spa...
void SetConvergenceCheck(bool setConvergenceCheck_=true)
Add a check for convergence after applying Mult.
void InitMPITeams(const MPI_Comm &comm, const int nDevs)
Initialize the AmgX library and create MPI teams based on the number of devices on each node nDevs....
virtual void Mult(const Vector &b, Vector &x) const
Utilize the AmgX library to solve the linear system where the "matrix" is the AMG approximation to th...
void ReadParameters(const std::string config, CONFIG_SRC source)
Read in the AmgX parameters either through a file or directly through a properly formated string....
void InitExclusiveGPU(const MPI_Comm &comm)
Initialize the AmgX library in parallel mode with exactly one GPU per rank after the solver configura...
T Max() const
Find the maximal element in the array, using the comparison operator < for class T.
Definition array.cpp:68
int Size() const
Return the logical size of the array.
Definition array.hpp:144
Definition solvers.hpp:513
virtual void SetOperator(const Operator &op)
Also calls SetOperator for the preconditioner if there is one.
Definition solvers.hpp:526
virtual void Mult(const Vector &b, Vector &x) const
Iterative solution of the linear system using the Conjugate Gradient method.
Definition solvers.cpp:718
A coefficient that is constant across space and time.
The MFEM Device class abstracts hardware devices such as GPUs, as well as programming models such as ...
Definition device.hpp:123
void Print(std::ostream &out=mfem::out)
Print the configuration of the MFEM virtual device object.
Definition device.cpp:286
Class for domain integration .
Definition lininteg.hpp:109
Collection of finite elements from the same family in multiple dimensions. This class is used to matc...
Definition fe_coll.hpp:27
virtual const char * Name() const
Definition fe_coll.hpp:79
Arbitrary order H1-conforming (continuous) finite elements.
Definition fe_coll.hpp:260
The BoomerAMG solver in hypre.
Definition hypre.hpp:1691
Wrapper for hypre's ParCSR matrix class.
Definition hypre.hpp:388
static void Init()
Initialize hypre by calling HYPRE_Init() and set default options. After calling Hypre::Init(),...
Definition hypre.hpp:74
void SetRelTol(real_t rtol)
Definition solvers.hpp:209
virtual void SetPreconditioner(Solver &pr)
This should be called before SetOperator.
Definition solvers.cpp:173
virtual void SetPrintLevel(int print_lvl)
Legacy method to set the level of verbosity of the solver output.
Definition solvers.cpp:71
void SetMaxIter(int max_it)
Definition solvers.hpp:211
Mesh data type.
Definition mesh.hpp:56
Array< int > bdr_attributes
A list of all unique boundary attributes used by the Mesh.
Definition mesh.hpp:282
void Clear()
Clear the contents of the Mesh.
Definition mesh.hpp:730
int GetNE() const
Returns number of elements.
Definition mesh.hpp:1226
int Dimension() const
Dimension of the reference space used within the elements.
Definition mesh.hpp:1160
void GetNodes(Vector &node_coord) const
Definition mesh.cpp:8973
void UniformRefinement(int i, const DSTable &, int *, int *, int *)
Definition mesh.cpp:10970
static int WorldRank()
Return the MPI rank in MPI_COMM_WORLD.
static int WorldSize()
Return the size of MPI_COMM_WORLD.
static void Init(int &argc, char **&argv, int required=default_thread_required, int *provided=nullptr)
Singleton creation with Mpi::Init(argc, argv).
Pointer to an Operator of a specified type.
Definition handle.hpp:34
OpType * As() const
Return the Operator pointer statically cast to a specified OpType. Similar to the method Get().
Definition handle.hpp:104
Jacobi smoothing for a given bilinear form (no matrix necessary).
Definition solvers.hpp:313
virtual void RecoverFEMSolution(const Vector &X, const Vector &b, Vector &x)
Reconstruct a solution vector x (e.g. a GridFunction) from the solution X of a constrained linear sys...
Definition operator.cpp:148
void Parse()
Parse the command-line options. Note that this function expects all the options provided through the ...
void PrintUsage(std::ostream &out) const
Print the usage message.
void PrintOptions(std::ostream &out) const
Print the options.
void AddOption(bool *var, const char *enable_short_name, const char *enable_long_name, const char *disable_short_name, const char *disable_long_name, const char *description, bool required=false)
Add a boolean option and set 'var' to receive the value. Enable/disable tags are used to set the bool...
Definition optparser.hpp:82
bool Good() const
Return true if the command line options were parsed successfully.
Class for parallel bilinear form.
Abstract parallel finite element space.
Definition pfespace.hpp:29
void GetEssentialTrueDofs(const Array< int > &bdr_attr_is_ess, Array< int > &ess_tdof_list, int component=-1) const override
HYPRE_BigInt GlobalTrueVSize() const
Definition pfespace.hpp:285
Class for parallel grid function.
Definition pgridfunc.hpp:33
void Save(std::ostream &out) const override
Class for parallel linear form.
Class for parallel meshes.
Definition pmesh.hpp:34
void Print(std::ostream &out=mfem::out, const std::string &comments="") const override
Definition pmesh.cpp:4801
Base class for solvers.
Definition operator.hpp:683
Vector data type.
Definition vector.hpp:80
int dim
Definition ex24.cpp:53
int main()
HYPRE_Int HYPRE_BigInt
real_t b
Definition lissajous.cpp:42
real_t a
Definition lissajous.cpp:41
const int visport
bool UsesTensorBasis(const FiniteElementSpace &fes)
Return true if the mesh contains only one topology and the elements are tensor elements.
Definition fespace.hpp:1345
const char vishost[]