import numpy as np
from scipy.special import h_roots
from dateutil.relativedelta import relativedelta
import datetime

def GHquad(n):
    """Gauss-Hermite quadrature weights"""
    Z, w = h_roots(n)
    return Z*np.sqrt(2), w/np.sqrt(np.pi)

def previous_twentieth(d):
    r = datetime.date(d.year, d.month, 20)
    if r > d:
        r -= relativedelta(months=1)
    mod = r.month % 3
    if mod != 0:
        r -= relativedelta(months = mod)
    return r