#!/usr/bin/python
# 9.4
import scipy as sp
def desired(Ts,rise,epsilon):
    Nr = rise/Ts
    omega = sp.pi/2/Nr
    rho = epsilon**(omega/sp.pi)
    phi = sp.array([1 -2*rho*sp.cos(omega), rho**2])
    dphi = len(phi)-1
    return phi, dphi