# Bazaar merge directive format 2 (Bazaar 0.90)
# revision_id: address@hidden
# target_branch: http://bzr.savannah.gnu.org/r/gsl/trunk/
# testament_sha1: 67e590a7828d424c9d6072833ce5f2805ae17186
# timestamp: 2012-01-14 17:09:23 +0200
# base_revision_id: address@hidden
#   nxlkxqc5due7nrk9
# 
# Begin patch
=== modified file 'ode-initval2/ChangeLog'
--- ode-initval2/ChangeLog	2011-06-28 16:45:45 +0000
+++ ode-initval2/ChangeLog	2012-01-14 15:05:08 +0000
@@ -1,3 +1,10 @@
+2012-01-14  Tuomo Keskitalo  <address@hidden>
+
+	* evolve.c: Modified initial derivative evaluation in evolve_apply
+	to reuse previously calculated values. This saves calls to the
+	user function. Thanks for Illes Farkas for pointing out redundant
+	function calls!
+
 2011-06-28  Brian Gough  <address@hidden>
 
 	* rk4imp.c (rk4imp_apply): use M_SQRT3 instead of sqrt(3) in array

=== modified file 'ode-initval2/evolve.c'
--- ode-initval2/evolve.c	2011-04-29 18:47:48 +0000
+++ ode-initval2/evolve.c	2012-01-14 15:05:08 +0000
@@ -138,16 +138,24 @@
 
   DBL_MEMCPY (e->y0, y, e->dimension);
 
-  /* Calculate initial dydt once if the method can benefit. */
-
+  /* Calculate initial dydt once or reuse previous value if the method
+     can benefit. */
+  
   if (step->type->can_use_dydt_in)
     {
-      int status = GSL_ODEIV_FN_EVAL (dydt, t0, y, e->dydt_in);
+      if (e->count == 0)
+	{
+	  int status = GSL_ODEIV_FN_EVAL (dydt, t0, y, e->dydt_in);
 
-      if (status)
-        {
-          return status;
-        }
+	  if (status)
+	    {
+	      return status;
+	    }
+	}
+      else
+	{
+	  DBL_MEMCPY (e->dydt_in, e->dydt_out, e->dimension);
+	}
     }
 
 try_step:

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