# HG changeset patch
# User Ben Abbott  <bpabbott@mac.com>
# Date 1340063643 14400
# Node ID 1d83d1539b2b696388367ba15da6d4dc8a2e1b70
# Parent  1230d5d58d2d1796be72d127f306449e4488b913
Fix plotyy to function as expected with "hold on" (Bug # 36508)

* scripts/plot/plotyy.m: Add new subfunction update_nextplot().
Synchronize the "nextplot" properties.  Add demo.

diff --git a/scripts/plot/plotyy.m b/scripts/plot/plotyy.m
--- a/scripts/plot/plotyy.m
+++ b/scripts/plot/plotyy.m
@@ -91,6 +91,7 @@
       ax = ax(1:2);
     elseif (length (ax) == 1)
       ax(2) = axes ();
+      set (ax(2), "nextplot", get (ax(1), "nextplot"))
     elseif (isempty (ax))
       ax(1) = axes ();
       ax(2) = axes ();
@@ -156,6 +157,7 @@
     axes (ax(2));
   else
     ax(2) = axes ();
+    set (ax(2), "nextplot", get (ax(1), "nextplot"))
   endif
   newplot ();
 
@@ -172,7 +174,6 @@
   set (ax(2), "yaxislocation", "right");
   set (ax(2), "ycolor", getcolor (h2(1)));
 
-
   if (strcmp (get(ax(1), "activepositionproperty"), "position"))
     set (ax(2), "position", get (ax(1), "position"));
   else
@@ -208,6 +209,8 @@
   addlistener (ax(2), "plotboxaspectratio", {@update_position, ax(1)});
   addlistener (ax(1), "plotboxaspectratiomode", {@update_position, ax(2)});
   addlistener (ax(2), "plotboxaspectratiomode", {@update_position, ax(1)});
+  addlistener (ax(1), "nextplot", {@update_nextplot, ax(2)});
+  addlistener (ax(2), "nextplot", {@update_nextplot, ax(1)});
 
   ## Store the axes handles for the sister axes.
   if (ishandle (ax(1)) && ! isprop (ax(1), "__plotyy_axes__"))
@@ -261,10 +264,24 @@
 %! clf;
 %! x = linspace (-1, 1, 201);
 %! hax = plotyy (x, sin (pi*x), x, cos (pi*x));
-%! ylabel ('Blue on the Left');
+%! ylabel (hax(1), 'Blue on the Left');
 %! ylabel (hax(2), 'Green on the Right');
 %! xlabel ('xlabel');
 
+%!demo
+%! clf
+%! hold on
+%! t = (0:0.1:9);
+%! x = sin (t);
+%! y = 5 * cos (t);
+%! [hax, h1, h2] = plotyy (t, x, t, y);
+%! [~, h3, h4] = plotyy (t+1, x, t+1, y);
+%! set ([h3, h4], "linestyle", "--")
+%! xlabel (hax(1), 'xlabel')
+%! title (hax(2), 'title')
+%! ylabel (hax(1), 'Left axis is Blue')
+%! ylabel (hax(2), 'Right axis is Green')
+
 function deleteplotyy (h, d, ax2, t2)
   if (ishandle (ax2) && strcmp (get (ax2, "type"), "axes")
       && (isempty (gcbf()) || strcmp (get (gcbf(), "beingdeleted"),"off"))
@@ -274,6 +291,19 @@
   endif
 endfunction
 
+function update_nextplot (h, d, ax2)
+  persistent recursion = false;
+  prop = "nextplot";
+  if (! recursion)
+    unwind_protect
+      recursion = true;
+      set (ax2, prop, get (h, prop));
+    unwind_protect_cleanup
+      recursion = false;
+    end_unwind_protect
+  endif
+endfunction
+
 function update_position (h, d, ax2)
   persistent recursion = false;