X-Git-Url: https://git.creatis.insa-lyon.fr/pubgit/?p=CreaPhase.git;a=blobdiff_plain;f=octave_packages%2Fsignal-1.1.3%2Fellip.m;fp=octave_packages%2Fsignal-1.1.3%2Fellip.m;h=5bfb3abd835ca47892bbfbccb2f36cc384ba6d3e;hp=0000000000000000000000000000000000000000;hb=f5f7a74bd8a4900f0b797da6783be80e11a68d86;hpb=1705066eceaaea976f010f669ce8e972f3734b05

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+## Copyright (C) 2001 Paulo Neis <p_neis@yahoo.com.br>
+## Copyright (C) 2003 Doug Stewart <dastew@sympatico.ca>
+##
+## This program is free software; you can redistribute it and/or modify it under
+## the terms of the GNU General Public License as published by the Free Software
+## Foundation; either version 3 of the License, or (at your option) any later
+## version.
+##
+## This program is distributed in the hope that it will be useful, but WITHOUT
+## ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+## FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
+## details.
+##
+## You should have received a copy of the GNU General Public License along with
+## this program; if not, see <http://www.gnu.org/licenses/>.
+
+## 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).
+
+
+function [a,b,c,d] = ellip(n, Rp, Rs, W, varargin)
+
+  if (nargin>6 || nargin<4) || (nargout>4 || nargout<2)
+    print_usage;
+  endif
+
+  ## interpret the input parameters
+  if (!(length(n)==1 && n == round(n) && n > 0))
+    error ("ellip: filter order n must be a positive integer");
+  endif
+
+
+  stop = 0;
+  digital = 1;  
+  for i=1:length(varargin)
+    switch varargin{i}
+    case 's', digital = 0;
+    case 'z', digital = 1;
+    case { 'high', 'stop' }, stop = 1;
+    case { 'low',  'pass' }, stop = 0;
+    otherwise,  error ("ellip: expected [high|stop] or [s|z]");
+    endswitch
+  endfor
+
+  [r, c]=size(W);
+  if (!(length(W)<=2 && (r==1 || c==1)))
+    error ("ellip: frequency must be given as w0 or [w0, w1]");
+  elseif (!(length(W)==1 || length(W) == 2))
+    error ("ellip: only one filter band allowed");
+  elseif (length(W)==2 && !(W(1) < W(2)))
+    error ("ellip: first band edge must be smaller than second");
+  endif
+
+  if ( digital && !all(W >= 0 & W <= 1))
+    error ("ellip: critical frequencies must be in (0 1)");
+  elseif ( !digital && !all(W >= 0 ))
+    error ("ellip: critical frequencies must be in (0 inf)");
+  endif
+
+  if (Rp < 0)
+    error("ellip: passband ripple must be positive decibels");
+  endif
+
+  if (Rs < 0)
+    error("ellip: stopband ripple must be positive decibels");
+  end
+
+
+  ##Prewarp the digital frequencies
+  if digital
+    T = 2;       # sampling frequency of 2 Hz
+    W = tan(pi*W/T);
+  endif
+
+  ##Generate s-plane poles, zeros and gain
+  [zero, pole, gain] = ncauer(Rp, Rs, n);
+
+  ## splane frequency transform
+  [zero, pole, gain] = sftrans(zero, pole, gain, W, stop);
+
+  ## Use bilinear transform to convert poles to the z plane
+  if digital
+    [zero, pole, gain] = bilinear(zero, pole, gain, T);
+  endif
+
+
+  ## convert to the correct output form
+  if nargout==2, 
+    a = real(gain*poly(zero));
+    b = real(poly(pole));
+  elseif nargout==3,
+    a = zero;
+    b = pole;
+    c = gain;
+  else
+    ## output ss results 
+    [a, b, c, d] = zp2ss (zero, pole, gain);
+  endif
+
+endfunction
+
+%!demo
+%! clc
+%! disp('---------------------------> NELLIP 0.2 EXAMPLE <-------------------------')
+%! x=input("Let's calculate the filter order: [ENTER]");
+%! disp("")
+%! x=input("[n, Ws] = ellipord([.1 .2],.4,1,90); [ENTER]");
+%! [n, Ws] = ellipord([.1 .2],.4,1,90)
+%! disp("")
+%! x=input("Let's calculate the filter: [ENTER]");
+%! disp("")
+%! x=input("[b,a]=ellip(5,1,90,[.1,.2]);  [ENTER]");
+%! [b,a]=ellip(5,1,90,[.1,.2])
+%! disp("")
+%! x=input("Let's calculate the frequency response: [ENTER]");
+%! disp("")
+%! x=input("[h,w]=freqz(b,a);  [ENTER]");
+%! [h,w]=freqz(b,a);
+%! 
+%! xlabel("Frequency");
+%! ylabel("abs(H[w])[dB]");
+%! axis([0,1,-100,0]);
+%! plot(w./pi, 20*log10(abs(h)), ';;')
+%! 
+%! hold('on');
+%! x=ones(1,length(h));
+%! plot(w./pi, x.*-1, ';-1 dB;')
+%! plot(w./pi, x.*-90, ';-90 dB;')
+%! hold('off');
+%! 
+%! xlabel("")
+%! ylabel("")
+%! clc