function [ta,y] = operate(t,x,s,d)
% OPERATE Time scaling and time shifting operations for CT signals.
%
%         [TN,YN] = OPERATE(t,x,A,B) generates time and signal values for
%         x(A*t+B) from given values of t and x(t).
%	  DEFAULT VALUES: B=0 if not specified. A=1 if not bspecified.
%
%         [TN,YN] = OPERATE(t,x,A) generates time and signal values for
%         x(A*t) from given values of t and x(t). [Default value: A=1]
%
%         OPERATE (with no input arguments) invokes the following example:
%
%           % First generate x(t)=u(t+1)-r(t)+r(t-1) 
%	    % Then sketch  x(t) and  x(0.5t-2)
%           >>t=-4:.02:4;
%           >>x=ustep(t+1)-uramp(t)+uramp(t-1);
%           >>[t1,x1]=operate(t,x,0.5,-2);
%           >>plot(t,x,t1,x1)


% 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: akambard@mtu.edu
% Copyright (c) 1998


if nargin==0,
 help operate
 disp('Strike a key to see results of the example')
 pause
 t=-4:.02:4;
 x=ustep(t+1)-uramp(t)+uramp(t-1);
 [t1,x1]=operate(t,x,.5,-2);
  v=matverch;
 if v < 4, eval('clg');else,eval('clf');end

 axis([-4 12 0 2])
 plot(t,x,t1,x1)
 axis([-4 12 0 2])
 grid
 hold off
 return
end

if nargin > 1 & nargin < 5,

 if nargin<4,
  d=0;
 end

 if nargin<3,
  s=1;
 end

 ta=(t-d)/s;
 if nargout>1,
  y=x;
  if s<0,
   ta=fliplr(ta);
   y=fliplr(y);
  end
 end
 
elseif nargin == 1,
 error('Not enough input arguments');
elseif nargin > 4,
 error('Too many input arguments');
end