besstf.m

很多matlab的源代码

function [a,b] = besstf(n)
% BESSTF Transfer function of normalized Bessel filters.
%
%	[NUM,DEN] = BESSTF(N) Transfer function of Nth order Bessel filter 
%	N = filter order
%       NUM, DEN contain num and den of H(s) in descending powers of s.
%
%       BESSTF (with no input arguments) invokes the following example:
%
%	% Find the transfer function of a 5th order normalized Bessel filter
%         >>[nn,dd] = besstf(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 besstf,disp('Strike a key to see results of the example')
pause,[nn,dd]=besstf(5),return,end

b=ones(1,n+1);
k=3:2:2*n-1;b(1)=b(1)*prod(k);ii=1;
for i=1:n-1,
k=n-i+1:2*n-i;
b(i+1)=b(i+1)*prod(k);
ii=i*ii;b(i+1)=b(i+1)/(2^(n-i))/ii;
end
a=b(1);b=b(n+1:-1:1);