code changes by Sonu Sharma during FOSSEE Fellowship 2018

1 files changed, 91 insertions, 34 deletions

diff --git a/macros/cheb2ord.sci b/macros/cheb2ord.sci
index 815ba0d..27ca7e6 100644
--- a/macros/cheb2ord.sci
+++ b/macros/cheb2ord.sci
@@ -1,36 +1,93 @@
+// Copyright (C) 2018 - IIT Bombay - FOSSEE
+//
+// This file must be used under the terms of the CeCILL.
+// This source file is licensed as described in the file COPYING, which
+// you should have received as part of this distribution.  The terms
+// are also available at
+// http://www.cecill.info/licences/Licence_CeCILL_V2-en.txt
+// Original Source : https://octave.sourceforge.io/signal/
+// Modifieded by:Sonu Sharma, RGIT Mumbai
+// Organization: FOSSEE, IIT Bombay
+// Email: toolbox@scilab.in
+
 function [n, Wc] = cheb2ord(Wp, Ws, Rp, Rs)
-//This function computes the minimum filter order of a Chebyshev type II filter with the desired response characteristics. 
-//Calling Sequence
-//n = cheb2ord(Wp, Ws, Rp, Rs)
-//[n, Wc] = cheb2ord(Wp, Ws, Rp, Rs)
-//Parameters 
-//Wp: scalar or vector of length 2, all elements must be in the range [0,1]
-//Ws: scalar or vector of length 2, all elements must be in the range [0,1]
-//Rp: real value
-//Rs: real value
-//Description
-//This is an Octave function.
-//This function computes the minimum filter order of a Chebyshev type II filter with the desired response characteristics. 
-//Stopband frequency ws and passband frequency wp specify the the filter frequency band edges. 
-//Frequencies are normalized to the Nyquist frequency in the range [0,1]. 
-//Rp is measured in decibels and is the allowable passband ripple and Rs is also measured in decibels and is the minimum attenuation in the stop band.
-//If ws>wp then the filter is a low pass filter. If wp>ws, then the filter is a high pass filter.
-//If wp and ws are vectors of length 2, then the passband interval is defined by wp and the stopband interval is defined by ws. 
-//If wp is contained within the lower and upper limits of ws, the filter is a band-pass filter. If ws is contained within the lower and upper limits of wp, the filter is a band-stop or band-reject filter.
-//Examples
-//cheb2ord([0.25,0.3],[0.2,0.8],0.3,0.4)
-//ans =  1
-
-rhs = argn(2)
-lhs = argn(1)
-if(rhs~=4)
-error("Wrong number of input arguments.")
-end
-
-	select(lhs)
-	case 1 then
-	n = callOctave("cheb2ord",Wp,Ws,Rp,Rs)
-	case 2 then
-	[n,Wc] = callOctave("cheb2ord",Wp,Ws,Rp,Rs)
-	end
+    //Minimum filter order of a digital Chebyshev type II filter with the desired response characteristics.
+
+    //Calling Sequence
+    //n = cheb2ord(Wp, Ws, Rp, Rs)
+    //[n, Ws] = cheb2ord(Wp, Ws, Rp, Rs)
+
+    //Parameters
+    //Wp: scalar or vector of length 2 (passband edge(s)), all elements must be in the range [0,1]
+    //Ws: scalar or vector of length 2 (stopband edge(s)), all elements must be in the range [0,1]
+    //Rp: passband ripple in dB.
+    //Rs: stopband attenuation in dB.
+    //n: Minimum order of filter satisfying given specs.
+
+    //Description
+    //This function computes the minimum filter order of a Chebyshev type II filter with the desired response characteristics.
+    //Stopband frequency ws and passband frequency wp specify the the filter frequency band edges.
+    //Frequencies are normalized to the Nyquist frequency in the range [0,1].
+    //Rp is measured in decibels and is the allowable passband ripple and Rs is also measured in decibels and is the minimum attenuation in the stop band.
+    //If ws>wp then the filter is a low pass filter. If wp>ws, then the filter is a high pass filter.
+    //If wp and ws are vectors of length 2, then the passband interval is defined by wp and the stopband interval is defined by ws.
+    //If wp is contained within the lower and upper limits of ws, the filter is a band-pass filter. If ws is contained within the lower and upper limits of wp, the filter is a band-stop or band-reject filter.
+
+    //Examples
+    //Wp = 40/500;
+    //Ws = 150/500;
+    //Rp = 3;
+    //Rs = 60;
+    //[n,Ws] = cheb2ord(Wp,Ws,Rp,Rs)
+    //Output :
+    // Ws  =
+    //
+    //    0.3
+    // n  =
+    //
+    //    4.
+    //
+
+    funcprot(0);
+    [nargout nargin] = argn();
+
+    if nargin ~= 4
+        error("cheb2ord: invalid number of inputs")
+    else
+        validate_filter_bands ("cheb2ord", Wp, Ws);
+    end
+
+    T = 2;
+
+    // returned frequency is the same as the input frequency
+    Wc = Ws;
+
+    // warp the target frequencies according to the bilinear transform
+    Ws = (2/T)*tan(%pi*Ws./T);
+    Wp = (2/T)*tan(%pi*Wp./T);
+
+    if (Wp(1) < Ws(1))
+        // low pass
+        if (length(Wp) == 1)
+            Wa = Wp/Ws;
+        else
+            // FIXME: Implement band reject filter type
+            error ("cheb2ord: band reject is not yet implemented");
+        end
+    else
+        // if high pass, reverse the sense of the test
+        if (length(Wp) == 1)
+            Wa = Ws/Wp;
+        else
+            // band pass
+            Wa=(Wp.^2 - Ws(1)*Ws(2))./(Wp*(Ws(1)-Ws(2)));
+        end;
+    end;
+    Wa = min(abs(Wa));
+
+    // compute minimum n which satisfies all band edge conditions
+    stop_atten = 10^(abs(Rs)/10);
+    pass_atten = 10^(abs(Rp)/10);
+    n = ceil(acosh(sqrt((stop_atten-1)/(pass_atten-1)))/acosh(1/Wa));
+
 endfunction