% demonstrate action of 2x2 matrix on unit disc
% barnett 9/30/08

n = 100;                    % resolution of representing the circle
A = [1 2; 3 4];             % pick your matrix

t = (0:n)*2*pi/n;           % set of thetas
x = [cos(t); sin(t)];       % each col is a 2-vec on the unit circle
figure; plot(x(1,:), x(2,:), '-'); axis equal;
y = A*x;                    % apply matrix to each 2-vec, in one go
hold on;  plot(y(1,:), y(2,:), 'r-')