FDM Boundary-Correction API¶

Python API¶

The complete runnable example is in the numbered example section below; the exact callable fields and arguments are in the numbered API section. These values are copied from the current Python contract, not inferred from the UI.

Symbols and SI units¶

All geometric lengths use \(\mathrm{m}\); dimensionless selectors use \(1\).

Assumptions and validity¶

Authoring validation does not prove mesh generation or solver qualification; the realized report is authoritative.

1. What it is and when to use it¶

FDM.boundary_correction selects the embedded-boundary policy used by FDM operators: none is the binary-mask baseline, volume is the T0 volume-fraction correction, and full is the T1 boundary-stencil and demagnetization correction when the selected lane advertises it.

2. Physical and mathematical explanation¶

This is a numerical correction policy, not a new physical interaction. It changes how partially occupied boundary cells contribute to the discrete operator while leaving authored geometry and cell size unchanged.

3. Example - complete Python script¶

# %% FDM boundary correction policy
import fullmag as fm

nm = 1.0e-9
study = fm.study("fdm_boundary_correction")
study.engine("fdm")
study.device("cpu", precision="double")
study.mode("strict")
study.fdm(
    default_cell=(2 * nm, 2 * nm, 2 * nm),
    boundary_correction="volume",
    boundary_phi_floor=0.05,
    boundary_delta_min=0.2 * nm,
)
body = study.geometry(fm.Box(40 * nm, 20 * nm, 4 * nm), name="film")
body.Ms = 800.0e3
body.Aex = 13.0e-12
body.m = fm.texture.uniform(1.0, 0.0, 0.0)
study.stages.add_relax(stage_id="relax", algorithm="llg_overdamped", dt=5e-13, max_steps=100)

study.fdm(...) is the source-backed route for these low-level fields; ordinary uniform sizing should use study.objects.mesh.defaults(...).

4. Exact API¶

FDM.__init__(*, cell=None, default_cell=None, per_magnet=None, demag=None, projection_policy=None, boundary_correction=None, boundary_phi_floor=None, boundary_delta_min=None) rejects conflicting cell aliases, invalid modes, non-positive cells, out-of-range phi floors, and negative delta minima.

ProblemIR¶

The request lowers to the mesh-workflow or discretization subtree; requested intent remains distinct from the resolved mesh asset and provenance report.

Round-trip and failure semantics¶

Requested intent is the Python policy; resolved execution is the realized mesh report. Validation errors identify the violated domain rule, and unsupported combinations fail explicitly without silent fallback.

Discrete realization¶

The backend consumes the realized Cartesian or finite-element asset, including topology, markers, quality, and provenance where available.

5. How to set it in Control Room¶

Route: Model Explorer -> Study -> Discretization -> FDM. The current global authoring route is partial. Apply the FDM policy only where the draft exposes the correction keys; mesh and dependent solver resources then become stale. not implemented: frontend support for a dedicated typed editor for boundary_phi_floor and boundary_delta_min when they are absent from the current draft. See Control Room capability register.

6. Backend and frontend support¶

Validation¶

Focused constructor, lowering, and mesh-report tests are the evidence boundary for this page.

7. Limitations and known pitfalls¶

• Construction does not prove that a correction kernel executed.

• full may be rejected by interaction, geometry, precision, or device capability.

• A rejected correction must not silently become none or a CPU fallback.

8. Scientific bibliography¶

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

9. Source-code index¶

Source-code index¶

• Python contract source: packages/fullmag-py/src/fullmag/model/discretization.py and packages/fullmag-py/src/fullmag/world.py, where applicable. Backend realization is in the relevant backends/fdm or backends/fem lane named by the page.