function eignmovy(A,n,s)
%
% Call sequences: eignmovy (self-demonstrating) 
% eignmovy(A), eignmovy(A,n), eignmovy(A,n,s)
%
%  This program visualizes eigenvectors 
% for 2x2 matrices. A is a 2x2 matrix.
% n is optional and determines the number
% of vectors drawn. The third (optional)
% parameter determines the number of times
% that the movie is played.
% It is based on an idea by Gilbert Strang:
% As a reference see the CMJ vol.26,no4,
% September 1995, p.316 (S. Schonefeld).
% Typical examples use the matrices:
% A=[13 9;3 7]/8; (fairly generic)
% A=[cos(pi/4) -sin(pi/4);sin(pi/4) cos(pi/4)];
%                 (nonreal eigenvalues)
% A=[2 -2; -1 1]; (one zero eigenvalue)
% A=[2-sqrt(3) -3; 1 2+sqrt(3)]/2; (double e.value)
%
% Written by M.Kawski, October 1995
% Display colors etc updated August 1999
% http://math.la.asu.edu/~kawski
%
% SHOULD be reworked using double buffering and slow-down.

if nargin == 0
   A=[13 9;3 7]/8;
   end;
if nargin < 3 
   s=3;
   end;
if nargin < 2 
   n=120;
   end;
%  E=moviein(n+1);
phi=2*pi/n;
z=zeros(1,n+1);
x=cos(phi*[0:n]);
y=sin(phi*[0:n]);
v=A(1,:)*[x;y];
w=A(2,:)*[x;y];
m=max([1,max(abs(v)),max(abs(w))]);
clf
plot(x,y,'y-',v,w,'g-');
axis([-m,m,-m,m])
axis equal
axis('on');
whitebg([0 0 0])
hold on
p=plot([0;x(1)],[0;y(1)],'m-',...
       [0;v(1)],[0;w(1)],'c-'); 
%    hold on   
for j=1:s
for i=1:n+1
%   hold off
    set(p(1),'XData',[0;x(i)],'YData',[0;y(i)]);
    set(p(2),'XData',[0;v(i)],'YData',[0;w(i)]);
    drawnow
%   E(:,i)=getframe;
    end;
    end;
%movie(E,s,3);