rohitg00/ai-engineering-from-scratch · error · ValueError

horizon undefined: slope w={w} is ~0 (b={b}, p={p}, logit={l

Error message

horizon undefined: slope w={w} is ~0 (b={b}, p={p}, logit={logit})

What it means

Error "horizon undefined: slope w={w} is ~0 (b={b}, p={p}, logit={logit})" thrown in rohitg00/ai-engineering-from-scratch.

Source

Thrown at phases/15-autonomous-systems/21-metr-external-evaluation/code/main.py:76

            p = sigmoid(w * math.log(t) + b)
            err = p - y
            dw += err * math.log(t)
            db += err
        w -= lr * dw / n
        b -= lr * db / n
    return w, b


def horizon_at(w: float, b: float, p: float) -> float:
    """Expert time where P(success) = p.  sigmoid(w*log(t)+b) = p ->
    log(t) = (logit(p) - b) / w."""
    logit = math.log(p / (1 - p))
    # A zero (or near-zero) slope means success probability does not
    # depend on task length, so the horizon is undefined. Raise rather
    # than silently returning inf/nan so callers see a loud failure.
    eps = 1e-12
    if abs(w) < eps:
        raise ValueError(
            f"horizon undefined: slope w={w} is ~0 "
            f"(b={b}, p={p}, logit={logit})"
        )
    return math.exp((logit - b) / w)


# ---------- Eval-context gaming simulator ----------

def inject_gaming(tasks: list[tuple[float, bool]],
                  gaming_rate: float) -> list[tuple[float, bool]]:
    """Flip `gaming_rate` fraction of failures to successes (model behaves
    better in eval context). Returns a new list."""
    gamed = []
    for t, s in tasks:
        if not s and random.random() < gaming_rate:
            gamed.append((t, True))
        else:
            gamed.append((t, s))

View on GitHub (pinned to 39ea8a1c6d)

When it happens

Trigger: Thrown at phases/15-autonomous-systems/21-metr-external-evaluation/code/main.py:76 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of rohitg00/ai-engineering-from-scratch@39ea8a1c6d (2026-08-26). Data as JSON: /api/errors/290553a0298f442d. Report an issue: GitHub.