cmbemu

A CMB power-spectrum emulator competition: pre-generated training/test data, Wishart-likelihood scoring, and a CPU timing harness built on classy_sz / classy_szfast.

Install

pip install cmbemu

Requires Python ≥ 3.12.

Quickstart

import cmbemu as cec

# 1. Fetch the competition data (cached under ~/.cache/cmbemu)
train = cec.load_train()
test  = cec.load_test()

# 2. Define your emulator: any object exposing predict(dict) -> dict
class MyEmulator:
    def predict(self, params: dict):
        # params keys: omega_b, omega_cdm, H0, tau_reio, ln10^{10}A_s, n_s
        # return dict with keys tt/te/ee (len 6001) and pp (len 3001)
        ...

emu = MyEmulator()

# 3. Score it
result = cec.get_score(emu)
print(result["combined_S"], result["mae_total"]["mae"])

See idea.md for the competition rules and data_description.md for the dataset schema.

The scoring API

Three parallel entry points, one per component of the score:

acc  = cec.get_accuracy_score(emu)       # precision only
tim  = cec.get_time_score(emu)           # timing only
full = cec.get_score(emu)                # both + combined_S

What combined_S is

The single scalar leaderboard number. With $E$ = mae_total (the precision MAE), $T$ = mean CPU time per call in ms, $T_0$ = t_floor_ms (default 1 ms), $\alpha$ = alpha (default 1):

$$ S ;=; \log_{10}(E) ,+, \alpha \cdot \log_{10}(\max(T,, T_0)) $$

Lower is better. Above the floor, one decade of precision trades for one decade of speed; sub-millisecond inference buys no further credit (MCMC per-step overhead dominates below that scale).

Precision and speed are cleanly decomposed: you can recompute combined_S from the two sub-scores yourself:

acc = cec.get_accuracy_score(emu)
tim = cec.get_time_score(emu)
S   = cec.combined_score(acc["mae_total"]["mae"], tim["t_cpu_ms_mean"])

See idea.md for the full Wishart derivation, block decomposition, and rationale for MAE over MSE.

CPU timing setup

Timing is done CPU-only, single-threaded, warm, with fresh parameters at every call (no result caching possible). Before importing your emulator:

export JAX_PLATFORMS=cpu
export CUDA_VISIBLE_DEVICES=

Pass strict_cpu=True to get_time_score / get_score to make the check a hard failure rather than a warning.

Generate more data (optional)

Want to study how your architecture's precision scales with $N_\text{train}$? Draw more cosmologies from the same prior:

extra = cec.generate_data(n=20_000, seed=42, save_to="extra.npz")

Baselines

Two trivial emulators ship with the package for sanity checks:

emu1 = cec.ConstantPlanck()                    # always returns Planck fiducial
emu2 = cec.NearestNeighbour(cec.load_train())  # 1-NN lookup on training set

Expected ConstantPlanck → combined_S ≈ 7.05 on the full test set. Any real emulator should beat this on precision by many decades.

Project layout

• src/cmbemu/ — the installable package
• scripts/ — internal dataset-building and diagnostic tools
• idea.md — competition pitch
• data_description.md — dataset schema + loading patterns
• STATUS.md — current state of the competition design