--- loncom/homework/default_homework.lcpm	2005/03/29 17:57:51	1.96
+++ loncom/homework/default_homework.lcpm	2005/03/31 14:43:13	1.97
@@ -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 1.96 2005/03/29 17:57:51 albertel Exp $
+# $Id: default_homework.lcpm,v 1.97 2005/03/31 14:43:13 albertel Exp $
 #
 # Copyright Michigan State University Board of Trustees
 #
@@ -518,10 +518,14 @@ sub format {
     #if ($options =~ /\$/) { $dollamode=1; }
     #if ($options =~ /,/)  { $commamode=1; }
     if ($options =~ /\./) { $alwaysperiod=1; }
-    $fmt=~s/e/E/g;
-    my $result=sprintf('%.'.$fmt,$value);
-    if ($alwaysperiod && $fmt eq '0f') { $result .='.'; }
-    $result=~s/(E[+-]*)0/$1/;
+    if ($fmt=~/s$/i) {
+	$result=&format_significant_figures($value,$fmt);
+    } else {
+	$fmt=~s/e/E/g;
+	my $result=sprintf('%.'.$fmt,$value);
+	if ($alwaysperiod && $fmt eq '0f') { $result .='.'; }
+	$result=~s/(E[+-]*)0/$1/;
+    }
     #if ($dollarmode) {$result=&dollarformat($result);}
     #if ($commamode) {$result=&commaformat($result);}
     return $result;
@@ -585,7 +589,11 @@ sub prettyprint {
     if ($options =~ /\$/) { $dollarmode=1; }
     if ($options =~ /,/)  { $commamode=1; }
     if ($options =~ /\./) { $alwaysperiod=1; }
-    if ($fmt) { $value=sprintf('%.'.$fmt,$value); }
+    if ($fmt=~/s$/i) {
+	$value=&format_significant_figures($value,$fmt);
+    } elsif ($fmt) {
+	$value=sprintf('%.'.$fmt,$value);
+    }
     if ($alwaysperiod && $fmt eq '0f') {
 	if ($target eq 'tex') {
 	    $value .='\\ensuremath{.}';
@@ -647,6 +655,36 @@ sub dollarformat {
     return $number; 
 }
 
+# format of form ns or nS where n is an integer
+sub format_significant_figures {
+    my ($number,$format) = @_; 
+    return '0' if ($number == 0);
+    # extract number of significant figures needed
+    my ($sig) = ($format =~ /(\d+)s/i);
+    # arbitrary choice - suggestions ?? or throw error message?
+    $sig = 3 if ($sig eq '');
+    # save the minus sign
+    my $sign = ($number < 0) ? '-' : '';
+    $number = abs($number);
+    # needed to correct for a number greater than 1 (or
+    my $power = ($number < 1) ? 0 : 1;
+    # 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.
+    my $xsig = $number*10**($sig-$x10-$power);
+    # get just digits left of decimal pt - also rounds off correctly
+    my $xint  = sprintf('%.0f',$xsig);
+    # save any trailing zero's
+    my ($zeros) = ($xint =~ /(0+)$/);
+    # return number to original magnitude
+    my $numSig = $xint*10**($x10-$sig+$power);
+    # insert trailing zero's if have decimal point
+    $numSig =~ s/^(\d+)\.(\d+)(\e?(.*)?)$/$1\.$2$zeros$3/;
+    # return number with sign
+    return $sign.$numSig;
+
+}
+
 sub map {
     my ($phrase,$dest,$source)=@_;
     my @oldseed=&random_get_seed();