function DrawRect(a,b,L,W,c)
% Adds a rectangle to the current window.
% Assumes hold is on.
% The rectangle has vertices (a,b), (a+L,b), (a+L,b+W),
% and (a,b+W) and color c where c is one of 'r', 'g', 'y', etc.

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