--- loncom/homework/functionplotresponse.pm	2010/11/13 03:22:58	1.37
+++ loncom/homework/functionplotresponse.pm	2010/11/13 22:30:28	1.38
@@ -1,7 +1,7 @@
 # LearningOnline Network with CAPA
 # option list style responses
 #
-# $Id: functionplotresponse.pm,v 1.37 2010/11/13 03:22:58 www Exp $
+# $Id: functionplotresponse.pm,v 1.38 2010/11/13 22:30:28 www Exp $
 #
 # Copyright Michigan State University Board of Trustees
 #
@@ -417,7 +417,7 @@ sub start_functionplotrule {
                                      $token,'8').
              &Apache::edit::text_arg('Optional maximum length for range:','maximumlength',
                                      $token,'8').'<br />'.
-             &Apache::edit::select_arg(&mt('Relationship:'),'relationship',
+             &Apache::edit::select_or_text_arg(&mt('Relationship:'),'relationship',
                                   [['eq','equal'],
                                    ['ne','not equal'],
                                    ['ge','greater than or equal'],
@@ -595,7 +595,11 @@ sub d2dt2_cubic_hermite {
 #
 sub array_index {
    my ($xmin,$xmax,$x)=@_;
-   return int(($x-$xmin)/($xmax-$xmin)*400.+0.5);
+   if ($x ne '') {
+      return int(($x-$xmin)/($xmax-$xmin)*400.+0.5);
+   } else {
+      return undef;
+   }
 }
 
 #
@@ -886,7 +890,7 @@ sub functionplotrulecheck {
 # Basic sanity checks
    if ($li<0) { $li=0; }
    if ($lh>400) { $lh=400; }
-   if ($li>$lh) {
+   if (($li>$lh) || (!defined($lh))) {
        $lh=$li;
    }