--- a/doc/interpreter/plotimages.m
+++ b/doc/interpreter/plotimages.m
@@ -48,6 +48,15 @@
     z = linspace (0, 1, numel (t));
     plot3 (r.*sin(t), r.*cos(t), z);
     print (strcat (nm, ".", typ), strcat ("-d", typ))    
+  elseif (strcmp (nm, "extended"))
+    x = 0:0.01:3;
+    plot(x,erf(x));
+    hold on;
+    plot(x,x,"r");
+    axis([0, 3, 0, 1]);
+    text(0.65, 0.6175, strcat('\leftarrow x = {2/\surd\pi {\fontsize{16}',
+      '\int_{\fontsize{8}0}^{\fontsize{8}x}} e^{-t^2} dt} = 0.6175'))
+    print (strcat (nm, ".", typ), strcat ("-d", typ))
   else
     error ("unrecognized plot requested");
   endif