def _update_pdf(population, fitnesses, pdfs, quantile):
    """Find a better pdf, based on fitnesses."""
    # First we determine a fitness threshold based on a quantile of fitnesses
    fitness_threshold = _get_quantile_cutoff(fitnesses, quantile)

    # Then check all of our possible pdfs with a stochastic program
    return _best_pdf(pdfs, population, fitnesses, fitness_threshold)
Find a better pdf, based on fitnesses.