Caveats

Read these before interpreting any number. They are physics/design facts, not bugs.

Frozen-seed large-scale offset

All 64 design models share five initial-condition seeds, so the ensemble-mean ξ (and ξ_hh) amplitudes at r ≳ 30 Mpc/h carry a frozen ~+2–3 % offset vs truth. Confirmed at two independent-seed fiducials (F5n1 and F6n1: signed ξ_hh bands +1.7–2.6 % over [2.5, 60] at both) — so it is the design offset, not an emulator defect.

• pk_mm is CLOSED — the low-k anchor to linear theory removes it.
• xi_mm / xi_hh remain OPEN — an r-space anchor and a Hankel-of-anchored-P(k) hybrid were both tested and rejected (they degrade the BAO).
• Design-internal comparisons are unaffected (the offset is common-mode).

Details: DOCUMENTATION.md §12; mitigation campaign in fRn1_new_runs_plan.md.

ξ near the BAO zero crossing

ξ fractional errors are meaningless where |ξ| < 0.01. The suite masks there and quotes χ vs the across-box SEM instead. Don't divide by ξ in that band.

xi_hh small-r validity radii

In route="exact", each mass-bin pair carries a validity radius res["validity"]["r_valid_bin"][i, j] (1.4–2.9 Mpc/h for ΛCDM, up to ~5 for f(R) heavy pairs): halo exclusion — haloes cannot overlap — means there is no signal to predict below it. The returned values there are a flat continuation of the boundary prediction (never NaN); respect r_valid_bin in any quantitative use. Routes have validity windows: exact [1.3, 100] (per-pair floors), bbar [20, 70] Mpc/h. Requested r below ~1.25 or above the xi_mm support (124.8) raises.

Velocity moments

• Accuracy is χ = residual / SEM, never fractional (the moments cross zero).
• f(R) high even moments (c40, c04, c22, c02) sit well above χ = 1 at design interior — a design-sampling limit; use with care and consult return_var (per-emulator χ in the manifest).
• Mass range: the 13-bin grid spans log₁₀M ∈ [12.5, 14.2]; the high-mass cap is signal-to-noise motivated. vel_binned mass edges must lie on the grid (whole-bin aggregation keeps it exact).

Redshift coverage

Only z = 0.25 (all properties) and z = 0.00 (matter sector: hmf, pk_mm, xi_mm) are registered. Other redshifts raise — the registry snaps only within Z_TOL = 0.005.

Parameter conventions

• θ order is fixed: [Omega_m, h, n_s, S_8(, logf_R0)].
• Pass S_8, not σ_8. S_8 = sigma_8 * sqrt(Omega_m / 0.3).
• Outside the design ranges the GP extrapolates and is unvalidated.

Provenance

When in doubt, the manifest is the source of truth: reg.entry(prop, gravity, z) gives the accuracy block, dependency pins, and the code version that produced the trained emulator.