set old_style on
xsetech(frect=[0,0,10,10])
xrect(0,10,10,10)
n=100;
xset('pixmap',1)
driver('X11');
for k=-n:n,
  a=ones(n,n);
  a= 3*tril(a,k)+ 2*a;
  a= a + a';
  k1= 3*(k+100)/200;
  Matplot1(a,[k1,2,k1+7,9])
  xset('wshow')
  xset('wwpc')
end
xset('pixmap',0)