Data commit

Task/Cumulative-standard-deviation/Perl/cumulative-standard-deviation-1.pl

@@ -0,0 +1,37 @@
+{
+    package SDAccum;
+    sub new {
+	my $class = shift;
+	my $self = {};
+	$self->{sum} = 0.0;
+	$self->{sum2} = 0.0;
+	$self->{num} = 0;
+	bless $self, $class;
+	return $self;
+    }
+    sub count {
+	my $self = shift;
+	return $self->{num};
+    }
+    sub mean {
+	my $self = shift;
+	return ($self->{num}>0) ? $self->{sum}/$self->{num} : 0.0;
+    }
+    sub variance {
+	my $self = shift;
+	my $m = $self->mean;
+	return ($self->{num}>0) ? $self->{sum2}/$self->{num} - $m * $m : 0.0;
+    }
+    sub stddev {
+	my $self = shift;
+	return sqrt($self->variance);
+    }
+    sub value {
+	my $self = shift;
+	my $v = shift;
+	$self->{sum} += $v;
+	$self->{sum2} += $v * $v;
+	$self->{num}++;
+	return $self->stddev;
+    }
+}

Task/Cumulative-standard-deviation/Perl/cumulative-standard-deviation-2.pl

@@ -0,0 +1,7 @@
+my $sdacc = SDAccum->new;
+my $sd;
+
+foreach my $v ( 2,4,4,4,5,5,7,9 ) {
+    $sd = $sdacc->value($v);
+}
+print "std dev = $sd\n";

Task/Cumulative-standard-deviation/Perl/cumulative-standard-deviation-3.pl

@@ -0,0 +1,14 @@
+# <(x - <x>)²> = <x²> - <x>²
+{
+    my $num, $sum, $sum2;
+    sub stddev {
+	my $x = shift;
+	$num++;
+	return sqrt(
+	    ($sum2 += $x**2) / $num -
+	    (($sum += $x) / $num)**2
+	);
+    }
+}
+
+print stddev($_), "\n" for qw(2 4 4 4 5 5 7 9);

Task/Cumulative-standard-deviation/Perl/cumulative-standard-deviation-4.pl

@@ -0,0 +1 @@
+perl -MMath::StdDev -e '$d=new Math::StdDev;foreach my $v ( 2,4,4,4,5,5,7,9 ) {$d->Update($v); print $d->variance(),"\n"}'

Task/Cumulative-standard-deviation/Perl/cumulative-standard-deviation-5.pl

@@ -0,0 +1,6 @@
+use Math::StdDev;
+$d=new Math::StdDev;
+foreach my $v ( 2,4,4,4,5,5,7,9 ) {
+  $d->Update($v);
+  print $d->variance(),"\n"
+}