function DrawRect(a,b,L,W,c)
% Add a rectangle to the current window, assuming hold is on.
% The rectangle has its lower left vertex at (a,b), length L,
% width W, and color c where c is one of 'r', 'g', 'y', etc.,
% or a rgb vector (e.g., [.2 1 .5]).

x = [a a+L a+L a a];
y = [b b b+W b+W b];
fill(x,y,c);
