scalemixture.py 文件源码

def inv_digamma_minus_log(y, tol=1e-10, n_iter=100):
    """
    Solve y = psi(alpha) - log(alpha) for alpha by fixed point
    integration.
    """
    if y >= -log(6.):
        x = 1 / (2 * (1 - exp(y)))
    else:
        x = 1.e-10
    for _i in range(n_iter):
        z = approx_psi(x) - log(x) - y
        if abs(z) < tol:
            break
        x -= x * z / (x * d_approx_psi(x) - 1)
        x = abs(x)
    return x