code changes by Sonu Sharma during FOSSEE Fellowship 2018

1 files changed, 87 insertions, 37 deletions

diff --git a/macros/buttord.sci b/macros/buttord.sci
index 2a17521..dbf0e10 100644
--- a/macros/buttord.sci
+++ b/macros/buttord.sci
@@ -1,39 +1,89 @@
+// 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] = buttord(Wp, Ws, Rp, Rs)
-///This function computes the minimum filter order of a Butterworth filter with the desired response characteristics. 
-//Calling Sequence
-//n = buttord(Wp, Ws, Rp, Rs)
-//[n, Wc] = buttord(Wp, Ws, Rp, Rs)
-//Parameters 
-//Wp: scalar or vector of length 2
-//Ws: scalar or vector of length 2, elements must be in the range [0,1]
-//Rp: real or complex value
-//Rs: real or complex value
-//Description
-//This is an Octave function.
-//This function computes the minimum filter order of a Butterworth filter with the desired response characteristics. 
-//The filter frequency band edges are specified by the passband frequency wp and stopband frequency ws.
-//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 in decibels and is the minimum attenuation in the stop band.
-//If ws>wp, the filter is a low pass filter. If wp>ws, the filter is a high pass filter.
-//If wp and ws are vectors of length 2, then the passband interval is defined by wp 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
-//[n, Wn] = buttord(Wp, Ws, 3, 60)
-//n =  5
-//Wn =  0.080038
-
-rhs = argn(2)
-lhs = argn(1)
-if(rhs~=4)
-error("Wrong number of input arguments.")
-end
-
-	select(lhs)
-	case 1 then
-	n = callOctave(Wp,Ws,Rp,Rs)
-	case 2 then
-	[n,Wc] = callOctave(Wp,Ws,Rp,Rs)
-	end
+    //Minimum filter order and 3dB cutoff frequency of a digital Butterworth filter with the desired response characteristics
+
+    //Calling Sequence
+    //n = buttord(Wp, Ws, Rp, Rs)
+    //[n, Wc] = buttord(Wp, Ws, Rp, Rs)
+
+    //Parameters
+    //Wp: scalar or vector of length 2 (passband edge(s) ), elements must be in the range [0,1]
+    //Ws: scalar or vector of length 2 (stopband edge(s) ), elements must be in the range [0,1]
+    //Rp: passband ripple in dB.
+    //Rs: stopband attenuation in dB.
+    //n: Minimum filter order satisfying specs
+    //Wc: 3dB cutoff frequency/frequencies
+
+    //Description.
+    //This function computes the minimum filter order of a Butterworth filter with the desired response characteristics.
+    //The filter frequency band edges are specified by the passband frequency wp and stopband frequency ws.
+    //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 in decibels and is the minimum attenuation in the stop band.
+    //If ws>wp, the filter is a low pass filter. If wp>ws, the filter is a high pass filter.
+    //If wp and ws are vectors of length 2, then the passband interval is defined by wp 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 ;
+    //[n, Wc] = buttord(Wp, Ws, 3, 60)
+    //Output :
+    // Wc  =
+    //
+    //    0.0800376
+    // n  =
+    //
+    //    5.
+
+    funcprot(0);
+    [nargout nargin] = argn();
+
+    if (nargin ~= 4)
+        error("buttord: invalid number of inputs");
+    else
+        validate_filter_bands ("buttord", Wp, Ws);
+    end
+
+    if (length (Wp) == 2)
+        warning ("buttord: seems to overdesign bandpass and bandreject filters");
+    end
+
+    T = 2;
+
+    // if high pass, reverse the sense of the test
+    stop = find(Wp > Ws);
+    Wp(stop) = 1-Wp(stop); // stop will be at most length 1, so no need to
+    Ws(stop) = 1-Ws(stop); // subtract from ones(1,length(stop))
+
+    // warp the target frequencies according to the bilinear transform
+    Ws = (2/T)*tan(%pi*Ws./T);
+    Wp = (2/T)*tan(%pi*Wp./T);
+
+    // compute minimum n which satisfies all band edge conditions
+    // the factor 1/length(Wp) is an artificial correction for the
+    // band pass/stop case, which otherwise significantly overdesigns.
+    qs = log(10^(Rs/10) - 1);
+    qp = log(10^(Rp/10) - 1);
+    n = ceil(max(0.5*(qs - qp)./log(Ws./Wp))/length(Wp));
+
+    // compute -3dB cutoff given Wp, Rp and n
+    Wc = exp(log(Wp) - qp/2/n);
+
+    // unwarp the returned frequency
+    Wc = atan(T/2*Wc)*T/%pi;
+
+    // if high pass, reverse the sense of the test
+    Wc(stop) = 1-Wc(stop);
+
 endfunction