--- loncom/homework/default_homework.lcpm	2011/06/09 15:43:56	1.159
+++ loncom/homework/default_homework.lcpm	2013/01/21 06:16:50	1.163
@@ -1,7 +1,7 @@
 # The LearningOnline Network with CAPA 
 # used by lonxml::xmlparse() as input variable $safeinit to Apache::run::run()
 #
-# $Id: default_homework.lcpm,v 1.159 2011/06/09 15:43:56 www Exp $
+# $Id: default_homework.lcpm,v 1.163 2013/01/21 06:16:50 raeburn Exp $
 #
 # Copyright Michigan State University Board of Trustees
 #
@@ -318,11 +318,13 @@ sub caparesponse_check_list {
 	    $responses->[0][-1]=$part1;
 	    $unit=&capa_formula_fix($part2);
             my $customunits=$LONCAPA::CAPAresponse_args{'customunits'};
-            foreach my $replacement (split(/\s*\,\s*/,$customunits)) {
-                my ($which,$what)=split(/\s*\=\s*/,$replacement);
-                if ((defined($which)) && (defined($what))) {
-                   $what=&capa_formula_fix($what);
-                   $unit=~s/$which/\($what\)/g;
+            if ($customunits =~ /\S/) {
+                foreach my $replacement (split(/\s*\,\s*/,$customunits)) {
+                    my ($which,$what)=split(/\s*\=\s*/,$replacement);
+                    if ((defined($which)) && (defined($what))) {
+                        $what=&capa_formula_fix($what);
+                        $unit=~s/$which/\($what\)/g;
+                    }
                 }
             }
 	}
@@ -357,7 +359,7 @@ sub caparesponse_check_list {
              $appendunit='%'.$appendunit;
           }
 # Zero does not need a dimension
-          if (($element==0) && ($unit!~/\w/) && ($answerunit=~/\w/)) {
+          if (($element =~ /^[0\.]+$/) && ($unit!~/\w/) && ($answerunit=~/\w/)) {
              $appendunit=$answerunit;
           }
 # Do the math for the student if allowed
@@ -814,6 +816,7 @@ sub cos { CORE::cos(shift) }
 sub exp { CORE::exp(shift) }
 sub int { CORE::int(shift) }
 sub log { CORE::log(shift) }
+sub ln { CORE::log(shift) }
 sub atan2 { CORE::atan2($_[0],$_[1]) }
 sub sqrt { CORE::sqrt(shift) }
 
@@ -1030,6 +1033,17 @@ sub format_significant_figures {
     $number = abs($number);
     # needed to correct for a number greater than 1 (or
     my $power = ($number < 1) ? 0 : 1;
+    if ($power && $number =~ /^\d+$/) {
+        my $nonzeros = $number;
+        $nonzeros =~ s/0+$//;
+        if (length($number) - length($nonzeros) > 1) {
+            # convert to exponential form
+            my $n = $sig-1;
+            my $numSig = sprintf('%.' . $n . 'E', $number);
+            # return number with sign
+            return $sign.$numSig;
+        }
+    }
     # could round up. Take the integer part of log10.
     my $x10 = int(log($number)/log(10));
     # find number with values left of decimal pt = # of sign figs.
@@ -1181,7 +1195,6 @@ sub middlename {
     return $middlename;
 }
 
-                                                                                
 sub lastname {
     my $lastname = &EXT('environment.lastname');
     $lastname = '' if $lastname eq "";