attn.m

很多matlab的源代码

function y =attn (ty,n,w,esq)
% ATTN Attenuation (in dB) of classical LP Filters.
%
%	Y = ATTN(TY,N,W,E2) attenuation of classical LOWPASS prototypes.
%	TY = 'bw','c1', and 'c2' (Butterworth, Chebyshev I, Chebyshev II)
%	N = order
%	W = array of normalized frequencies
%	E2 = epsilon squared (eps^2) (default: 1).
%	Y = attenuation in dB. Y is the same size as W
%
%       ATTN (with no input arguments) invokes the following example:
%       % Compute the attenuation of a 5th order Chebyshev filter 
%	% with eps^2=0.5 at the frequencies W = 1,1.5,2,2.5,3.
%	>>y = attn('c1',5,[1:.5:3],0.5)


% ADSP Toolbox: Version 2.0 
% For use with "Analog and Digital Signal Processing", 2nd Ed.
% Published by PWS Publishing Co.
%
% Ashok Ambardar, EE Dept. MTU, Houghton, MI 49931, USA
% http://www.ee.mtu/faculty/akambard.html
% e-mail: [e-mail]
% Copyright (c) 1998


if nargin == 0,
 help attn
 disp('strike a key to see results of above example')
 pause
 y = attn('c1',5,[1:.5:3],0.5)
 return
end

if nargin < 4, esq = 1; end

if ty == 'bw',
 y = 10*log10(1+esq*(w.^(2*n)));
elseif ty=='c1',
 y = 10*log10(1+esq*(chebyfun(n,w)).^2);
elseif ty == 'c2',
 y = 10*log10(1+(1)./(esq*(chebyfun(n,(1)./w)).^2));
else
 error('Unidentified filter type')
end