def _zpklp2lp(z, p, k, wo=<NUM_LIT:1.0>):
z = atleast_1d(z)<EOL>p = atleast_1d(p)<EOL>wo = float(wo)  <EOL>degree = _relative_degree(z, p)<EOL>z_lp = wo * z<EOL>p_lp = wo * p<EOL>k_lp = k * wo**degree<EOL>return z_lp, p_lp, k_lp<EOL>
Transform a lowpass filter prototype to a different frequency.

Return an analog low-pass filter with cutoff frequency `wo`
from an analog low-pass filter prototype with unity cutoff frequency,
using zeros, poles, and gain ('zpk') representation.

Parameters
----------
z : ndarray
    Zeros of the analog IIR filter transfer function.
p : ndarray
    Poles of the analog IIR filter transfer function.
k : float
    System gain of the analog IIR filter transfer function.
wo : float
    Desired cutoff, as angular frequency (e.g. rad/s).
    Defaults to no change.

Returns
-------
z : ndarray
    Zeros of the transformed low-pass filter transfer function.
p : ndarray
    Poles of the transformed low-pass filter transfer function.
k : float
    System gain of the transformed low-pass filter.

Notes
-----
This is derived from the s-plane substitution

.. math:: s \rightarrow \frac{s}{\omega_0}