def deltas(errors, epsilon, mean, std):
    """Compute mean and std deltas.

    delta_mean = mean(errors) - mean(all errors below epsilon)
    delta_std = std(errors) - std(all errors below epsilon)
    """
    below = errors[errors <= epsilon]
    if not len(below):
        return 0, 0

    return mean - below.mean(), std - below.std()