Imported ferromagnet FEM mesh¶

Problem statement¶

The supported study-level imported mesh contract is FEM(mesh=...), not a per-object source recipe.

Governing equations¶

Symbols and SI units¶

Assumptions and validity¶

The mesh path is study-level and must be nonempty. The current lazy Rust planner accepts .json MeshIR sources and validates them for execution. Python asset realization can dispatch supported file readers, but arbitrary formats, units, region ownership, or topology are not inferred safely.

Python API¶

The table is exhaustive for this public family entry point. Alias rows are alternatives, not extra simultaneous requirements.

# %% imports
import fullmag as fm
from pathlib import Path

nm = 1.0e-9

# %% stage-first study-level imported mesh hint
study = fm.study("imported_mesh_reference")
study.engine("fem")
study.device("cpu", precision="double")
study.mode("strict")
study.universe(mode="manual", size=(800 * nm, 400 * nm, 300 * nm))
study.universe.mesh(maximum_element_size=100 * nm)

body = study.geometry(fm.Box(300 * nm, 100 * nm, 5 * nm), name="film")
body.Ms = 800.0e3
body.Aex = 13.0e-12
body.m = fm.texture.uniform(1.0, 0.0, 0.0)

mesh_path = Path("meshes/ferromagnet.json")
mesh_kwargs = {
    "order": 1,
    "maximum_element_size": 2e-9,
}
if mesh_path.is_file():
    mesh_kwargs["source"] = str(mesh_path)
study.objects.mesh.defaults(
    **mesh_kwargs,
)

# The typed FEM value is the same study-level contract in isolation.
fem = fm.FEM(order=1, maximum_element_size=2e-9, mesh="meshes/ferromagnet.json")
fem_ir = fem.to_ir()
study.stages.add_relax(stage_id="equilibrium", dt=5.0e-13, max_steps=1)

ProblemIR¶

FEM.to_ir() emits {order, hmax, mesh} under backend_policy.discretization_hints.fem. The flat study resolver also constructs FEM(mesh=shared_source) for a shared study source. Per-object source is not this contract: PerObjectMeshRecipe.__post_init__ and GeometryMeshHandle.configure reject it and direct users to FEM(mesh=...).

Round-trip and failure semantics¶

Requested intent is FEM(order, maximum_element_size or hmax, mesh). Resolved execution is the loaded and validated MeshIR consumed by the FEM plan. Validation errors include missing/nonpositive size, order below one, empty path, unreadable JSON, malformed MeshIR, or invalid execution topology. Unsupported combinations fail closed: the current lazy planner accepts only .json mesh assets and reports other suffixes; it does not remesh or silently reinterpret them.

Discrete realization¶

realize_fem_mesh_asset prefers hints.mesh and dispatches generate_mesh_from_file; the Rust planner load_mesh_from_source loads .json, deserializes MeshIR, and runs execution validation. The realized topology and markers, not the file extension or hmax hint, determine backend consumption.

Implementation mapping¶

The source index maps public authoring, lowering, realization, reporting, and backend consumption. Source-backed FEM CPU support does not imply that every requested topology is supported; FEM GPU remains capability-gated by the realized mesh and active runtime.

Validation¶

Confirm source identity, requested and actual methods, typed cell families, complete region/boundary markers, zero inverted or degenerate cells, and the relevant quality distributions. Then refine the controlling size or layer count while holding geometry, materials, solver tolerances, and outputs fixed, and require convergence of a physical observable.

Limitations¶

There is no supported fm.PerObjectMeshRecipe(source=...) route. The maximum_element_size value remains a required FEM hint but does not rewrite an already loaded mesh. This page makes no automatic repair, unit conversion, marker synthesis, or topology conversion claim.

Scientific bibliography¶

• C. Geuzaine and J.-F. Remacle, “Gmsh: a three-dimensional finite element mesh generator with built-in pre- and post-processing facilities,” International Journal for Numerical Methods in Engineering 79 (2009), 1309-1331, doi:10.1002/nme.2579.

• C. Abert, “Micromagnetics and spintronics: models and numerical methods,” European Physical Journal B 92, 120 (2019), doi:10.1140/epjb/e2019-90599-6.

Source-code index¶

Scope and purpose¶

This page defines the public contract for imported FEM mesh assets. It is an authoring and implementation reference: the Python example, the serialized ProblemIR description, the implementation mapping, and the adjacent source map are the source-backed contract. A capability marked partial or not evaluated is not presented as a production guarantee.

Scientific and numerical model¶

The mesh or grid is a discrete approximation of the continuous domain. For a Cartesian partition, each spacing satisfies Delta_i = L_i / N_i; for a geometry-dependent FEM mesh, the requested local target is bounded by the active bulk, interface, boundary, and topology constraints. In compact form, h_target(x) = min(h_bulk(x), h_interface(x), h_boundary(x)). Length quantities use SI metres (m); counts, orders, and topology labels are dimensionless.

The equations and assumptions in the earlier physical-problem and governing-equations sections state the model-specific specialization. This section does not introduce a conversion from FEM to FDM, a hidden topology conversion, or a silent CPU fallback.

Parameters¶

The exact callable and argument names are the ones shown in the ## Python API section above. For this page the parameter family is mesh path, FEM order, and imported-mesh validation. Use the documented defaults, validation rules, and ProblemIR lowering exactly as shown; do not replace a canonical argument with an unlisted alias. Numerical lengths must be supplied in metres, and invalid positive-length, count, order, periodicity, or topology constraints must fail closed rather than being silently repaired.

Control Room workflow¶

In Control Room, select the engine and mesh workflow, enter the same values as the Python authoring example, inspect the planned mesh or grid report, and only then submit the run. The UI is a projection of the public contract: a missing control is not evidence that the backend accepts the option, and a visible control is not evidence that a production lane is enabled. When the page or capability register marks a field partial or not evaluated, keep the workflow explicitly bounded to the implemented path.

Diagnostics and failure semantics¶

A valid request must preserve the declared geometry, units, element or cell topology, and backend lane. Reject non-finite or non-positive lengths, invalid counts and orders, incompatible periodic or shared-boundary data, and unsupported topology combinations at the owning validation layer. Reports should retain requested and resolved values, source identity, and any capability gate. No diagnostic may hide a failed mesh realization by substituting another discretization.

Where this is implemented¶

The existing implementation-mapping and source-code-index sections identify the exact public authoring, ProblemIR, planner, realization, and runtime owners for this topic. The adjacent .source-map.json file is the machine-readable source of truth for those paths, symbols, responsibilities, backend matrix, and reviewed revision. Claims in this page must be updated together with that map when an owner moves.