Choosing a Solver

Last changes: Documentation changelog

FullMag has one physical problem contract and several execution realizations. You select the numerical backend with study.engine("fdm") or study.engine("fem"), and the device with study.device("cpu" | "gpu", precision="double"). The rest of the study stays the same.

Finite difference (FDM)

FDM represents the domain on a regular cell grid and computes demagnetization through a cell-averaged Newell tensor with FFT convolution.

Choose FDM when:

  • the geometry is well represented by a regular grid (cuboids, thin films, multilayer stacks),

  • you need open-boundary demagnetization with fast FFT convolution,

  • you want the grid-to-cell physical meaning of an FDM magnet (native cell_size resolution).

The canonical FDM pages are FDM tensor convolution and FFT demagnetization and FDM.

Finite element (FEM)

FEM discretizes the domain with an unstructured tetrahedral or prismatic mesh that conforms to the geometry, and solves demagnetization with a Poisson airbox or a boundary-element method.

Choose FEM when:

  • the geometry is curved, conformal, or imported from CAD and needs boundary-conforming elements,

  • you need a magnetic body plus an airbox for scalar-potential demagnetization,

  • you work with standard problems, eigenmode/spectral studies, or problems that benefit from MFEM/hypre/libCEED solvers.

The canonical FEM pages are FEM Poisson airbox solver and FEM discretization and mesh authoring.

CPU versus GPU

Both FDM and FEM expose CPU and GPU execution lanes. The device choice is request metadata; the runtime records the resolved device and precision in the result.

  • The local CPU runtime is the common validation path and is covered by the repository smoke and qualification scripts.

  • FDM CUDA and FEM GPU use managed CUDA runtimes through the repository recipes. Executed GPU evidence requires a recorded device identity in the result; presence of GPU source or a successful host build is not device-parity proof.

Support and qualification matrix

Each terminal page documents its own four-lane matrix for FDM CPU, FDM GPU, FEM CPU, and FEM GPU, including unsupported and unqualified states. Use those matrices as the authoritative support status instead of this summary:

See FDM tensor convolution and FFT demagnetization, FEM Poisson airbox solver, and Demagnetization for the terminal matrices.

Do not infer a solver is production-ready from its name or from source presence. Requested intent and resolved execution are kept separate, and the planner rejects unsupported engine/device/ interaction combinations instead of silently substituting them.

Control Room crosswalk

Use the authoring path stated in this guide, normally Model Explorer -> Objects followed by the relevant Geometry, Material, Physics, Mesh, or Stage panel. Any parameter shown in Python but not shown in that path is TODO: frontend support; do not describe it as configurable in the UI. See Control Room capability register.

Python/API crosswalk

The runnable Python example and exact argument contract are authoritative. If this guide is conceptual or does not contain a runnable example, it explicitly defers to the linked {doc}``/python-api/index page rather than duplicating an unverified signature.

Physics, limitations, and bibliography

Use the linked physics or numerical-methods page for governing equations and assumptions. This onboarding page does not add a new physical model. Bibliography: see the linked terminal API or physics page; no additional source is claimed here.

Source-code index

  • No new implementation symbol is introduced by this guide. The exact Python source symbol is owned by the linked terminal API page and the runnable example.