import numpy as np
import pymc as pm


def model(data):
    """Floor model: ignores age and fits one mean length."""
    y = np.asarray(data["length"], dtype=float)
    with pm.Model() as null_model:
        intercept = pm.Normal("intercept", mu=0.0, sigma=10.0)
        sigma = pm.HalfNormal("sigma", sigma=5.0)
        pm.Normal("length", mu=intercept, sigma=sigma, observed=y)
    return null_model