N-ellip 0.2.1
usage: [Zz, Zp, Zg] = ellip(n, Rp, Rs, Wp, stype,'s')

Generate an Elliptic or Cauer filter (discrete and contnuious).

[b,a] = ellip(n, Rp, Rs, Wp)
low pass filter with order n, cutoff pi*Wp radians, Rp decibels
of ripple in the passband and a stopband Rs decibels down.

[b,a] = ellip(n, Rp, Rs, Wp, 'high')
high pass filter with cutoff pi*Wp...

[b,a] = ellip(n, Rp, Rs, [Wl, Wh])
band pass filter with band pass edges pi*Wl and pi*Wh ...

[b,a] = ellip(n, Rp, Rs, [Wl, Wh], 'stop')
band reject filter with edges pi*Wl and pi*Wh, ...

[z,p,g] = ellip(...)
return filter as zero-pole-gain.

[...] = ellip(...,'s')
return a Laplace space filter, W can be larger than 1.

[a,b,c,d] = ellip(...)
return  state-space matrices

References:

- Oppenheim, Alan V., Discrete Time Signal Processing, Hardcover, 1999.
- Parente Ribeiro, E., Notas de aula da disciplina TE498 -  Processamento
Digital de Sinais, UFPR, 2001/2002.
- Kienzle, Paul, functions from Octave-Forge, 1999 (http://octave.sf.net).

Author: Paulo Neis 
Modified: Doug Stewart Feb. 2003