--- loncom/homework/default_homework.lcpm	2001/05/30 21:49:13	1.23
+++ loncom/homework/default_homework.lcpm	2001/05/31 20:47:50	1.24
@@ -7,6 +7,7 @@
 # Guy Albertelli
 #
 # 05/25/2001 H. K. Ng
+# 05/31/2001 H. K. Ng
 #
 $RANDOMINIT=0;
 $pi=atan2(1,1)*4;
@@ -123,6 +124,14 @@ sub tex {
   }
 }
 
+sub var_in_tex {
+  if ( $external::target eq "tex" ) {
+    return @_[0];
+  } else {
+    return "";
+  }
+}
+
 sub web {
   if ( $external::target eq "tex" ) {
     return @_[1];
@@ -135,6 +144,12 @@ sub web {
   }
 }
 
+sub html {
+  if ( $external::target eq "web" ) {
+    return @_[0];
+  }
+}
+
 sub problem {
   return '1';
 }
@@ -193,12 +208,6 @@ sub max {
     return pop @sorted;
 }
 
-sub html {
-  if ( $external::target eq "web" ) {
-    return @_[0];
-  }
-}
-
 sub roundto {
     my ($input,$n) = @_;
     return sprintf('%.'.$n.'f',$input);
@@ -273,18 +282,78 @@ sub sec {
 
 sub open_date { 
   my @dc = split(/\s+/,localtime(&EXT('resource.0.opendate')));
-  return $dc[0].', '.$dc[1].' '.$dc[2].', '.$dc[4].' at '.$dc[3];
+  return '' if ($dc[0] eq "Wed" and $dc[2] == 31 and $dc[4] == 1969);
+  my @hm = split(/:/,$dc[3]);
+  my $ampm = " am";
+  if ($hm[0] > 12) {
+    $hm[0]-=12;
+    $ampm = " pm";
+  }
+  return $dc[0].', '.$dc[1].' '.$dc[2].', '.$dc[4].' at '.$hm[0].':'.$hm[1].$ampm;
 }
 
 sub due_date { 
   my @dc = split(/\s+/,localtime(&EXT('resource.0.duedate')));
-  return $dc[0].', '.$dc[1].' '.$dc[2].', '.$dc[4].' at '.$dc[3];
+  return '' if ($dc[0] eq "Wed" and $dc[2] == 31 and $dc[4] == 1969);
+  my @hm = split(/:/,$dc[3]);
+  my $ampm = " am";
+  if ($hm[0] > 12) {
+    $hm[0]-=12;
+    $ampm = " pm";
+  }
+  return $dc[0].', '.$dc[1].' '.$dc[2].', '.$dc[4].' at '.$hm[0].':'.$hm[1].$ampm;
+#  return $dc[0].', '.$dc[1].' '.$dc[2].', '.$dc[4].' at '.$dc[3];
 }
 
 sub answer_date { 
   my @dc = split(/\s+/,localtime(&EXT('resource.0.answerdate')));
-  return $dc[0].', '.$dc[1].' '.$dc[2].', '.$dc[4].' at '.$dc[3];
- }
+  return '' if ($dc[0] eq "Wed" and $dc[2] == 31 and $dc[4] == 1969);
+  my @hm = split(/:/,$dc[3]);
+  my $ampm = " am";
+  if ($hm[0] > 12) {
+    $hm[0]-=12;
+    $ampm = " pm";
+  }
+  return $dc[0].', '.$dc[1].' '.$dc[2].', '.$dc[4].' at '.$hm[0].':'.$hm[1].$ampm;
+#  return $dc[0].', '.$dc[1].' '.$dc[2].', '.$dc[4].' at '.$dc[3];
+}
+
+sub array_moments {
+  my @input=@_;
+  my (@output,$N);
+  $N=scalar (@input);
+  $output[0]=$N;
+  if ($N <= 1) {
+    $output[1]=$input[0];
+    $output[1] = "Input array not defined" if ($N == 0);
+    $output[2]="variance undefined for N<=1";
+    $output[3]="skewness undefined for N<=1";
+    $output[4]="kurtosis undefined for N<=1";
+    return @output;
+  }
+  my $sum=0;
+  foreach my $line (@input) {
+    $sum+=$line;
+  }
+  $output[1] = $sum/$N;
+  my ($x,$sdev,$var,$skew,$kurt) = 0;
+  foreach my $line (@input) {
+    $x=$line-$output[1];
+    $var+=$x**2;
+    $skew+=$x**3;
+    $kurt+=$x**4;
+  }
+  $output[2]=$var/($N-1);
+  $sdev=sqrt($output[2]);
+  if ($sdev == 0) {
+     $output[3]="inf-variance=0";
+     $output[4]="inf-variance=0";
+     return @output;
+  }
+  $output[3]=$skew/($sdev**3*$N);
+  $output[4]=$kurt/($sdev**4*$N)-3;
+  return @output;
+}
 
 sub choose {
   my $num = $_[0];
@@ -299,7 +368,3 @@ sub choose {
 #print $a."\n".$b."\n";
 
 
-
-
-
-