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// 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)
//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
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