iztlong.m

很多matlab的源代码

function [y,n] = iztlong(b,a,N,ty)
% IZTLONG Inverse z-transform sequence by long division.
%
%	[Y,n] = IZTLONG(N,D,K,TY) Simulates IZT by long division. 
%	N,D = Num and Den of H(z) =  of N(z)/D(z) in descending order
%	TY='r' for rightsided or 'l' for leftsided (noncausal) [Default: 'r'].
%	K = number of IZT values required 
%	Y returns the IZT sequence
%	n returns the index of the values in Y 
%
%	IZTLONG (with no input arguments) invokes the following example:
%
%	% Find the first 5 terms of the causal IZT of H(z) = (z-4)/(z*z-z+1)
% 	  >>[y5,n5] = iztlong([1 -4],[1 -1 1],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 iztlong,disp('Strike a key to see results of the example')
pause,[y5,n5]=iztlong([1 -4],[1 -1 1],5),return,end

if nargin<4,ty='r';end,ty=ty(1);
while b(1)==0,b(1)=[];end,
while a(1)==0;a(1)=[];end,
ind=length(a)-length(b);
if ty~='r',
b=fliplr(b);a=fliplr(a);ia=0;ib=0;
while b(1)==0,b(1)=[];ib=ib+1;end,
while a(1)==0;a(1)=[];ia=ia+1;end,
ind=ia-ib;
end
y=filter(b,a,[1 zeros(1,N-1)]);
if ty=='r',n=(0:N-1)+ind;else,n=(0:-1:-(N-1))+ind;end