Source code for deltasigma._cancelPZ

# -*- coding: utf-8 -*-
# Module providing the cancelPZ function
# Copyright 2013 Giuseppe Venturini
# This file is part of python-deltasigma.
# python-deltasigma is a 1:1 Python replacement of Richard Schreier's 
# MATLAB delta sigma toolbox (aka "delsigma"), upon which it is heavily based.
# The delta sigma toolbox is (c) 2009, Richard Schreier.
# python-deltasigma is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# LICENSE file for the licensing terms.

"""Module providing the cancelPZ() function

from __future__ import division

import copy

import numpy as np
from scipy.signal import lti

[docs]def cancelPZ(arg1, tol=1e-6): """Cancel zeros/poles in a SISO transfer function. **Parameters:** arg1 : LTI system description Multiple descriptions are supported for the LTI system. If one argument is used, it is a scipy ``lti`` object. If more arguments are used, they should be arranged in a tuple, the following gives the number of elements in the tuple and their interpretation: * 2: (numerator, denominator) * 3: (zeros, poles, gain) * 4: (A, B, C, D) Each argument can be an array or sequence. tol : float, optional the absolute tolerance for pole, zero cancellation. Defaults to 1e-6. **Returns:** (z, p, k) : tuple A tuple containing zeros, poles and gain (unchanged) after poles, zeros cancellation. """ if not isinstance(arg1, lti): arg1 = lti(*arg1) z = copy.copy(arg1.zeros) p = copy.copy(arg1.poles) k = arg1.gain for i in range(max(z.shape) - 1, -1, -1): d = z[i] - p cancel = np.nonzero(np.abs(d) < tol)[0] if cancel.size: p = np.delete(p, cancel[0]) z = np.delete(z, i) return z, p, k