http://www.pisces-conservation.com/growthhelp/janoschek.htm
    
    Parameters
    ----------
    x: int
    a: float
    beta: float
    k: float
    delta: float

    Returns
    -------
    float
        a - (a - beta) * np.exp(-k*x**delta)

def janoschek(x, a, beta, k, delta):
    """http://www.pisces-conservation.com/growthhelp/janoschek.htm
    
    Parameters
    ----------
    x: int
    a: float
    beta: float
    k: float
    delta: float

    Returns
    -------
    float
        a - (a - beta) * np.exp(-k*x**delta)
    """
    return a - (a - beta) * np.exp(-k*x**delta)