Add a useful package (from Source forge) for octave

[CreaPhase.git] / octave_packages / signal-1.1.3 / ellipord.m

diff --git a/octave_packages/signal-1.1.3/ellipord.m b/octave_packages/signal-1.1.3/ellipord.m
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+## Copyright (C) 2001 Paulo Neis <p_neis@yahoo.com.br>
+##
+## 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/>.
+
+## usage: [n,wp] = ellipord(wp,ws, rp,rs)
+##
+## Calculate the order for the elliptic filter (discrete)
+## wp: Cutoff frequency
+## ws: Stopband edge
+## rp: decibels of ripple in the passband.
+## rs: decibels of ripple in the stopband.
+##
+## References: 
+##
+## - Lamar, Marcus Vinicius, Notas de aula da disciplina TE 456 - Circuitos 
+##   Analogicos II, UFPR, 2001/2002.
+
+function [n, Wp] = ellipord(Wp, Ws, Rp, Rs)
+
+  [rp, cp]=size(Wp);
+  [rs, cs]=size(Ws);
+  if ( !(length(Wp)<=2 && (rp==1 || cp==1) && length(Ws)<=2 && (rs==1 || cs==1)) )
+    error ("ellipord: frequency must be given as w0 or [w0, w1]");
+  elseif (!all(Wp >= 0 & Wp <= 1 & Ws >= 0 & Ws <= 1)) #####
+    error ("ellipord: critical frequencies must be in (0 1)");
+  elseif (!(length(Wp)==1 || length(Wp) == 2 & length(Ws)==1 || length(Ws) == 2))
+    error ("ellipord: only one filter band allowed");
+  elseif (length(Wp)==2 && !(Wp(1) < Wp(2)))
+    error ("ellipord: first band edge must be smaller than second");
+  elseif (length(Ws)==2 && !(length(Wp)==2))
+    error ("ellipord: you must specify band pass borders.");
+  elseif (length(Wp)==2 && length(Ws)==2 && !(Ws(1) < Wp(1) && Ws(2) > Wp(2)) )
+    error ("ellipord: ( Wp(1), Wp(2) ) must be inside of interval ( Ws(1), Ws(2) )");
+  elseif (length(Wp)==2 && length(Ws)==1 && !(Ws < Wp(1) || Ws > Wp(2)) )
+    error ("ellipord: Ws must be out of interval ( Wp(1), Wp(2) )");
+  endif
+
+  # sampling frequency of 2 Hz
+  T = 2;
+
+  Wpw = tan(pi.*Wp./T); # prewarp
+  Wsw = tan(pi.*Ws./T); # prewarp
+
+  ##pass/stop band to low pass filter transform:
+  if (length(Wpw)==2 && length(Wsw)==2)
+    wp=1;
+    w02 = Wpw(1) * Wpw(2);     # Central frequency of stop/pass band (square)
+    w3 = w02/Wsw(2);
+    w4 = w02/Wsw(1);
+    if (w3 > Wsw(1))
+      ws = (Wsw(2)-w3)/(Wpw(2)-Wpw(1));
+    elseif (w4 < Wsw(2))
+      ws = (w4-Wsw(1))/(Wpw(2)-Wpw(1));
+    else
+      ws = (Wsw(2)-Wsw(1))/(Wpw(2)-Wpw(1));
+    endif
+  elseif (length(Wpw)==2 && length(Wsw)==1)
+    wp=1;
+    w02 = Wpw(1) * Wpw(2);
+    if (Wsw > Wpw(2))
+      w3 = w02/Wsw;
+      ws = (Wsw - w3)/(Wpw(2) - Wpw(1));
+    else
+      w4 = w02/Wsw;
+      ws = (w4 - Wsw)/(Wpw(2) - Wpw(1));
+    endif
+  else
+    wp = Wpw;
+    ws = Wsw;
+  endif
+
+  k=wp/ws;
+  k1=sqrt(1-k^2);
+  q0=(1/2)*((1-sqrt(k1))/(1+sqrt(k1)));
+  q= q0 + 2*q0^5 + 15*q0^9 + 150*q0^13; %(....)
+  D=(10^(0.1*Rs)-1)/(10^(0.1*Rp)-1);
+
+  n=ceil(log10(16*D)/log10(1/q));
+endfunction