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Mesh And Geometry

The frontends support both generated meshes and imported meshes. The mesh must provide element connectivity, node coordinates, and boundary information that matches the PDE model boundary-condition IDs.

Mesh Responsibilities

The mesh object supplies:

  • physical coordinates and element connectivity;
  • element type and geometric dimension;
  • boundary group classification;
  • optional high-order or curved geometry data;
  • optional periodic boundary metadata;
  • partitioning input for MPI preprocessing.

The frontend preprocessing step converts this information into backend mesh and dmd binary data.

Generated Meshes

Many examples use frontend mesh helper functions. Exact helper names differ by language and example, but the resulting structure is the same.

mesh = mkmesh_square(16, 16, 1, 1, pde.porder, 1);
mesh.boundarycondition = [1; 1; 1; 1];

# Use the mesh helpers available in the Python frontend/examples.
# The output must fill mesh["p"], mesh["t"], and boundary metadata.
pde, mesh = initializeexasim()

pde, mesh = Exasim.initializeexasim()
# Use Exasim mesh helpers or assign mesh.p, mesh.t, and boundary metadata.

Imported Meshes

Imported meshes should be normalized to the same frontend mesh fields before calling exasim(...). For Gmsh-based workflows, configure pde.gmsh if the binary is not on PATH.

pde.gmsh = "/path/to/gmsh";
% Generate or import mesh, then set mesh.boundarycondition consistently.

Boundary Tagging

Boundary tagging is geometric in the frontend and semantic in the PDE model. The mesh decides which face belongs to which boundary group; the PDE model decides what that boundary group means physically.

Example:

tol = 1e-8;
mesh.boundaryexpr = {
    @(p) abs(p(:,2)) < tol, ...
    @(p) abs(p(:,1)-1) < tol
};
mesh.boundarycondition = [1; 2];

For robust results, boundary predicates should include tolerances and should be mutually consistent with the generated or imported mesh coordinates.

Curved Meshes

Curved geometry is represented through high-order geometry nodes such as mesh.dgnodes when used by an example. The polynomial order, geometry order, and model dimension fields in pde must be consistent with this data.

Assumption: the mesh geometry is independent of physicsparam in the current parameter-sweep workflow. If a parameter changes the geometry, regenerate and preprocess the mesh explicitly for that case.

Mesh Partitioning

pde.mpiprocs controls the number of MPI ranks used by preprocessing and runtime execution. Parallel runs produce rank-local datain and dataout files, and dmd records how to reconstruct global fields.

pde["mpiprocs"] = 4
sol, pde, mesh = exasim(pde, mesh)

For a parameter sweep with fixed mesh and fixed mpiprocs, master and dmd are reused across cases.

See Also