1 files changed, 85 insertions, 34 deletions
diff --git a/macros/cheb1ord.sci b/macros/cheb1ord.sci
index b2789bf..61737a0 100644
--- a/macros/cheb1ord.sci
+++ b/macros/cheb1ord.sci
@@ -1,36 +1,87 @@
+// 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] = cheb1ord(Wp, Ws, Rp, Rs)
-//This function computes the minimum filter order of a Chebyshev type I filter with the desired response characteristics. 
-//Calling Sequence
-//n = cheb1ord(Wp, Ws, Rp, Rs)
-//[n, Wc] = cheb1ord(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 I 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
-//cheb1ord(0.1,0.2,-0.3,4)
-//ans =  2
-
-rhs = argn(2)
-lhs = argn(1)
-if(rhs~=4)
-error("Wrong number of input arguments.")
-end
-
-	select(lhs)
-	case 1 then
-	n = callOctave("cheb1ord",Wp,Ws,Rp,Rs)
-	case 2 then
-	[n,Wc] = callOctave("cheb1ord",Wp,Ws,Rp,Rs)
-	end
+    //Minimum filter order of a digital Chebyshev type I filter with the desired response characteristics.
+
+    //Calling Sequence
+    //n = cheb1ord(Wp, Ws, Rp, Rs)
+    //[n, Wp] = cheb1ord(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 filter order satisfying specs
+    //Wp: passband edge(s)
+
+    //Description
+    //This function computes the minimum filter order of a Chebyshev type I 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
+    //[n, wp]=cheb1ord([0.25 0.3],[0.24 0.31],3,10)
+    // wp  =
+    //
+    //    0.25    0.3
+    // n  =
+    //
+    //    3.
+
+    funcprot(0);
+    [nargout nargin] = argn();
+
+    if nargin ~= 4
+        error("cheb1ord: invalid number of inputs");
+    else
+        validate_filter_bands ("cheb1ord", Wp, Ws);
+    end
+
+    T = 2;
+
+    // returned frequency is the same as the input frequency
+    Wc = Wp;
+
+    // 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 = Ws/Wp;
+        else
+            // FIXME: Implement band reject filter type
+            error ("cheb1ord: band reject is not yet implemented");
+        end;
+    else
+        // if high pass, reverse the sense of the test
+        if (length(Wp) == 1)
+            Wa = Wp/Ws;
+        else
+            // band pass
+            Wa=(Ws.^2 - Wp(1)*Wp(2))./(Ws*(Wp(1)-Wp(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(Wa));
+
 endfunction