def nig_prior(U_y0, sig0):
    """
    Returns parameter of normal inverse gamma prior according to 
    the choice in the paper. See Section 2.3.

    Arguments:
        U_y0 {float} -- uncertainty of parameter
        sig0 {float} -- standard deviation of measurement device

    Returns:
        tuple -- (\lambda, a, b)
    """    
    a = 1
    llambda = (0.28*U_y0/sig0)**2
    b = (sig0**2)/1.44
    return llambda, a, b