ibu-boost 0.1.1

GBDT with absolute-threshold screening split selection, accelerated by fused Triton kernels.

Screening Boosted Trees

Gradient-boosted decision trees where each candidate split is scored by an absolute relevance value derived from the screening transform introduced in "Screening Is Enough" (Nakanishi 2026).

Instead of selecting the relatively best split among all candidates, a node with max(ρ) == 0 emits no split at all — becoming a leaf without an external min_gain_to_split heuristic. The acceptance threshold is learnable.

Install

pip install ibu-boost          # NumPy reference only
pip install "ibu-boost[triton]" # + GPU Triton kernels (CUDA)

Windows GPU: installs triton-windows automatically — same API as upstream Triton.

Quick start

from ibu_boost import ScreeningBooster
from sklearn.datasets import fetch_california_housing
from sklearn.model_selection import train_test_split
import numpy as np

X, y = fetch_california_housing(return_X_y=True)
X_tr, X_te, y_tr, y_te = train_test_split(X, y, test_size=0.2, random_state=0)

model = ScreeningBooster(
    n_estimators=100, learning_rate=0.1, max_depth=6,
    tree_type="oblivious",   # CatBoost-style symmetric splits
    device="cuda",           # requires [triton] extra
)
model.fit(X_tr, y_tr.astype("float32"))
preds = model.predict(X_te)
rmse = float(np.sqrt(np.mean((y_te - preds) ** 2)))
print(f"RMSE: {rmse:.4f}")
print(f"Mean accept_rate: {model.mean_accept_rate():.1%}")

GPU performance (RTX 4060 Ti, California Housing, 100 rounds)

Backend	Train time	Speedup	RMSE
CPU (NumPy)	5.34 s	1x	0.5286 ± 0.0039
CUDA (Triton)	1.70 s	3.15x	0.5286 ± 0.0039

Kernel-level speedup (N=65536, F=8, B=255): 51x over NumPy. RMSE is numerically identical across backends.

Screening transform

raw_gain  = G_L²/(H_L+λ) + G_R²/(H_R+λ) − G_total²/(H_total+λ)
norm_gain = raw_gain / H_total          # N-invariant normalisation
s         = 1 − exp(−norm_gain / τ)    # bounded similarity ∈ [0, 1)
ρ         = max(1 − r·(1−s), 0)²       # Trim-and-Square

Parameters τ = exp(s_w) + ε and r = exp(s_r) + 1 are stored as log-scale scalars (ScreeningParams). They will become learnable in a future release.

Key features

• Absolute split rejection: max(ρ) == 0 → node becomes leaf automatically. No min_gain_to_split hyperparameter required.
• Oblivious tree mode (tree_type="oblivious"): CatBoost-style symmetric splits — all nodes at a depth share one (feature, bin). Fast GPU aggregation.
• Non-oblivious mode (tree_type="non_oblivious"): each node independently selects its best split (standard GBDT structure).
• Missing value handling: XGBoost-style learned default direction per split.
• Binary classification (objective="binary"): log-loss with sigmoid output.
• Screening diagnostics: model.mean_accept_rate() shows fraction of splits accepted — a real-time indicator of over/under-rejection.
• ScreeningParamSearch: K-fold grid search over (s_w, s_r).
• Triton GPU kernels: fused histogram scatter + screening transform; batched multi-node dispatch; full GPU pipeline (X/g/h pre-loaded, on-device normalisation).

Parameters

ScreeningBooster(
    n_estimators   = 100,          # boosting rounds
    learning_rate  = 0.1,
    max_depth      = 6,
    min_samples_leaf = 20,
    num_bins       = 255,          # quantile bins per feature
    params         = ScreeningParams(s_w=-2.0, s_r=-6.0, lam=1.0),
    tree_type      = "oblivious",  # or "non_oblivious"
    objective      = "regression", # or "binary"
    device         = "cpu",        # or "cuda"
)

Milestones

Milestone	Status
M0: NumPy reference + Triton skeleton	✅
M1: Single regression tree + diagnostics	✅
M2: Triton numerical consistency + LightGBM/XGBoost benchmark	✅
M3: Oblivious tree + binary classification	✅
M4: h normalisation + ScreeningParamSearch (K-fold grid tuner)	✅
M5: Missing value handling (XGBoost-style default direction)	✅
M6: Triton GPU kernels (histogram + screening fused)	✅
M7: Batched multi-node GPU dispatch + full GPU pipeline (3.15x E2E)	✅
Phase 2: Learnable (s_w, s_r) via differentiable surrogate	🔜

License

MIT © 2026 ibusan100