% ell.m  96/07/29
%
% Plot of ellipse in xy plane
%
% x^2/4+y^2=1
%

    t=2*pi*(0:50)/50;
    x=2*cos(t); y=sin(t);

    hold off;
    plot(x,y,'w-');  
    hold on;
    axis square;
    axis([-3 3 -3 3]);
    plot([0 0],[-3 3],'w-');
    plot([-3 3],[0 0],'w-');

    t=1;
    p=[2*cos(t); sin(t)]; 
    der=[-2*sin(t); cos(t)];
    tanvec=der/norm(der);
    plot(p(1),p(2),'o');
    arrow1(p,p+der,.2);
    arrow(p,p+tanvec,.2);

    xlabel('x');
    ylabel('y');

    text(.6,1.4,'T(t)');
    text(-.5,1.7,'r''(t)');

    hold off;
