def polynomial(voltage, order=50):
    """Generate the polynomial I-V curve model.

    From Kennedy (1999) [see full references in online docs].

    Args:
        voltage (ndarray): normalized bias voltage
        order (float): order of polynomial (usually between 30 and 50)

    Returns:
        ndarray: normalized current

    """
    current = voltage ** (2 * order + 1) / (1 + voltage ** (2 * order))
    return current
