def ellip(N, rp, rs, Wn, btype='<STR_LIT>', analog=False, output='<STR_LIT>'):
return iirfilter(N, Wn, rs=rs, rp=rp, btype=btype, analog=analog,<EOL>output=output, ftype='<STR_LIT>')<EOL>
Elliptic (Cauer) digital and analog filter design.

Design an Nth order digital or analog elliptic filter and return
the filter coefficients in (B,A) or (Z,P,K) form.

Parameters
----------
N : int
    The order of the filter.
rp : float
    The maximum ripple allowed below unity gain in the passband.
    Specified in decibels, as a positive number.
rs : float
    The minimum attenuation required in the stop band.
    Specified in decibels, as a positive number.
Wn : array_like
    A scalar or length-2 sequence giving the critical frequencies.
    For elliptic filters, this is the point in the transition band at
    which the gain first drops below -`rp`.
    For digital filters, `Wn` is normalized from 0 to 1, where 1 is the
    Nyquist frequency, pi radians/sample.  (`Wn` is thus in
    half-cycles / sample.)
    For analog filters, `Wn` is an angular frequency (e.g. rad/s).
btype : {'lowpass', 'highpass', 'bandpass', 'bandstop'}, optional
    The type of filter.  Default is 'lowpass'.
analog : bool, optional
    When True, return an analog filter, otherwise a digital filter is
    returned.
output : {'ba', 'zpk'}, optional
    Type of output:  numerator/denominator ('ba') or pole-zero ('zpk').
    Default is 'ba'.

Returns
-------
b, a : ndarray, ndarray
    Numerator (`b`) and denominator (`a`) polynomials of the IIR filter.
    Only returned if ``output='ba'``.
z, p, k : ndarray, ndarray, float
    Zeros, poles, and system gain of the IIR filter transfer
    function.  Only returned if ``output='zpk'``.

See also
--------
ellipord

Notes
-----
Also known as Cauer or Zolotarev filters, the elliptical filter maximizes
the rate of transition between the frequency response's passband and
stopband, at the expense of ripple in both, and increased ringing in the
step response.

As `rp` approaches 0, the elliptical filter becomes a Chebyshev
type II filter (`cheby2`).  As `rs` approaches 0, it becomes a Chebyshev
type I filter (`cheby1`).  As both approach 0, it becomes a Butterworth
filter (`butter`).

The equiripple passband has N maxima or minima (for example, a
5th-order filter has 3 maxima and 2 minima).  Consequently, the DC gain is
unity for odd-order filters, or -rp dB for even-order filters.

Examples
--------
Plot the filter's frequency response, showing the critical points:

>>> from scipy import signal
>>> import matplotlib.pyplot as plt

>>> b, a = signal.ellip(4, 5, 40, 100, 'low', analog=True)
>>> w, h = signal.freqs(b, a)
>>> plt.semilogx(w, 20 * np.log10(abs(h)))
>>> plt.title('Elliptic filter frequency response (rp=5, rs=40)')
>>> plt.xlabel('Frequency [radians / second]')
>>> plt.ylabel('Amplitude [dB]')
>>> plt.margins(0, 0.1)
>>> plt.grid(which='both', axis='both')
>>> plt.axvline(100, color='green') # cutoff frequency
>>> plt.axhline(-40, color='green') # rs
>>> plt.axhline(-5, color='green') # rp
>>> plt.show()