--- loncom/homework/functionplotresponse.pm	2010/10/17 22:32:19	1.14
+++ loncom/homework/functionplotresponse.pm	2010/10/19 02:04:27	1.15
@@ -1,7 +1,7 @@
 # LearningOnline Network with CAPA
 # option list style responses
 #
-# $Id: functionplotresponse.pm,v 1.14 2010/10/17 22:32:19 www Exp $
+# $Id: functionplotresponse.pm,v 1.15 2010/10/19 02:04:27 www Exp $
 #
 # Copyright Michigan State University Board of Trustees
 #
@@ -453,6 +453,40 @@ sub get_answer_from_form_fields {
    return ($answer,%coords);
 }
 
+#
+# The following functions calculate the cubic-hermite splines server-side
+#
+
+sub cubic_hermite {
+   my ($t,$p1,$s1,$p2,$s2)=@_;
+   return (2.*$t*$t*$t-3.*$t*$t+1.)*$p1 + 5.*($t*$t*$t-2.*$t*$t+$t)*($s1-$p1)+
+          (-2.*$t*$t*$t+3.*$t*$t)  *$p2 + 5.*($t*$t*$t-$t*$t)      *($s2-$p2);
+}
+
+#
+# d/dt(...)
+# 
+
+sub ddt_cubic_hermite {
+   my ($t,$p1,$s1,$p2,$s2)=@_;
+   return (6.*$t*$t-6.*$t) *$p1 + 5.*(3.*$t*$t-4.*$t+1.)*($s1-$p1)+
+          (-6.*$t*$t+6.*$t)*$p2 + 5.*(3.*$t*$t-2.*$t)   *($s2-$p2);
+}
+
+#
+# d^2/dt^2(...)
+#
+
+sub d2dt2_cubic_hermite {
+   my ($t,$p1,$s1,$p2,$s2)=@_;
+   return (12.*$t-6.) *$p1 + 5.*(6.*$t-4.)*($s1-$p1)+
+          (-12.*$t+6.)*$p2 + 5.*(6.*$t-2.)*($s2-$p2);
+}
+
+#
+# Implentation of <functionplotresponse>
+#
+
 sub start_functionplotresponse {
   my ($target,$token,$tagstack,$parstack,$parser,$safeeval,$style)=@_;
   my $result='';