µMAG Standard Problems¶

Problem definition¶

SP4 is a \(500 \times 125 \times 3\ \mathrm{nm}\) permalloy film with saturation magnetization \(M_s = 800\,000\ \mathrm{A\,m^{-1}}\), exchange stiffness \(A_{\mathrm{ex}} = 1.3 \times 10^{-11}\ \mathrm{J\,m^{-1}}\), and damping \(\alpha = 0.02\). An S-shaped magnetization state is relaxed, then one of two applied fields drives a dynamic reversal:

• field 1: \(\mathbf{B} = (-24.6, 4.3, 0)\ \mathrm{mT}\);

• field 2: \(\mathbf{B} = (-35.5, -6.3, 0)\ \mathrm{mT}\).

The canonical observable is the volume-weighted average of the reduced magnetization; the first zero-crossing of \(\bar m_x\) is compared against the NIST reference corpus (NIST is authoritative, MuMax3/OOMMF endpoint values are supplementary regression metrics only).

FullMag setup¶

• Meshes: magnetic element sizes \(3.0\), \(2.0\) and \(1.5\ \mathrm{nm}\); airboxes \(700^3\ \mathrm{nm}\) and \(1000 \times 500 \times 500\ \mathrm{nm}\) with airbox_hmax = 20 nm.

• SP4 relaxation uses a strict mixed-prism thin-film route in strict mode: film.mesh.thin_film(..., layers=1, topology="prismatic", exact_layers=True, transition="pyramid_to_tetrahedra", order=1). The topology-only mesh contract is in tests/standard_problems/mumag/sp4/fem/scenarios/mesh_single_prism_layer.py.

• Lanes: strict FEM CPU and strict FEM GPU in double precision; GPU demagnetization must resolve to device_hypre_poisson, never hybrid_cpu_poisson.

• Observables use native \(M_s \times V\) lumped-volume averages from scalars.csv; unweighted node averages are not accepted as the NIST observable.

• Uninterrupted trajectories are sampled every \(1\ \mathrm{ps}\); replay runs start from the same S-state and stop at the bracketing zero-crossing.

The public stage scenario is tests/standard_problems/mumag/sp4/fem/scenarios/relax_projected_gradient_bb.py, and the managed gate is:

just verify-fem-standard-problem-4

Standardowy wpis SP4 w układzie source-first (wprowadzony z kodu)¶

import fullmag as fm
from fullmag.select import in_object

study = fm.study("sp4_strict")
study.engine("fem")
study.device("cpu", precision="double")
study.mode("strict")

study.universe(
    mode="manual",
    size=(800e-9, 400e-9, 200e-9),
    center=(0.0, 0.0, 0.0),
    padding=(0.0, 0.0, 0.0),
)
study.universe.mesh(maximum_element_size=100e-9)

film = study.geometry(
    fm.Box(500e-9, 125e-9, 3e-9),
    name="film",
    object_id="film",
)
film.Ms = 800.0e3
film.Aex = 13.0e-12
film.m = fm.texture.uniform(1.0, 0.0, 0.0)
film.mesh(
    topology="prismatic",
    exact_layer_count=True,
    through_thickness_elements=1,
    through_thickness_distribution="fixed",
    transition_policy="pyramid_to_tetrahedra",
    order=1,
    mesh_strategy="swept_prism",
    sweep_face_meshing="triangular",
    sweep_direction="auto",
    element_family="prism",
)

frozen = fm.FrozenSpins(
    id="sp4_init_fixed",
    selector=in_object("film"),
    stage_ids=("relax",),
)
study.stages.add_relax(
    stage_id="relax",
    dt=5.0e-13,
    max_steps=1,
    constraints=(frozen,),
)

Current status¶

Relaxed S-state and reversal-run artifacts exist for FEM CPU and FEM GPU (coarse/baseline). The time-domain qualification record currently reports not_evaluated / unvalidated for the adaptive RK runs: artifact creation alone is not evidence of validation, and the dedicated NIST/convergence/CPU-GPU/no-fallback gate has not yet been closed. Do not treat this page as a claim that SP4 is physics-validated.

SP4 acceptance requires, per lane: NIST trajectory agreement, mesh and airbox convergence, CPU/GPU parity within the documented tolerances, and no silent fallback. Status advances only when the full managed gate passes.

Control Room crosswalk¶

Validation pages are inspection-only in Control Room. The UI may expose runtime metadata, fields, tables, or reports for inspection, but it does not create a qualification claim. TODO: frontend support applies to validation workflow authoring and report publication unless a specific control is named. See Control Room capability register.

Python/API crosswalk¶

Validation is not a standalone Python constructor unless the linked case page names one. Reproduce the exact case, inputs, device, precision, and receipt described by the page; use the referenced API pages for callable signatures.

Physics and bibliography scope¶

The page either states the governing benchmark model or delegates it to the linked physics/numerical-methods page. Any missing derivation is a documented boundary, not an implicit equation. Bibliography and source evidence remain the authoritative references listed by the validation case.

Source-code index¶

• No standalone implementation function is introduced by this validation page. Source evidence is the exact API, managed recipe, runtime manifest, and receipt named by the validation case.