=head1 NAME

Statistics::Basic::Variance - find the variance of a list

=head1 SYNOPSIS

Invoke it this way:

    my $variance = variance(1,2,3);

Or this way:

    my $v1  = vector(1,2,3);
    my $var = var($v1);

And then either query the values or print them like so:

    print "The variance of $v1: $variance\n";
    my $vq = $var->query;
    my $v0 = 0+$var;

Create a 20 point "moving" variance like so:

    use Statistics::Basic qw(:all nofill);

    my $sth = $dbh->prepare("select col1 from data where something");
    my $len = 20;
    my $var = var()->set_size($len);

    $sth->execute or die $dbh->errstr;
    $sth->bind_columns( my $val ) or die $dbh->errstr;

    while( $sth->fetch ) {
        $var->insert( $val );
        if( defined( my $v = $var->query ) ) {
            print "Variance: $v\n";
        }

        # This would also work:
        # print "Variance: $v\n" if $var->query_filled;
    }

=head1 METHODS

=over 4

=item B<new()>

The constructor takes a list of values, a single array ref, or a
single L<Statistics::Basic::Vector> as arguments.  It returns a
L<Statistics::Basic::Variance> object.

Note: normally you'd use the L<mean()|Statistics::Basic/variance() var()>
constructor, rather than building these by hand using C<new()>.

=item B<query_mean()>

Returns the L<Statistics::Basic::Mean> object used in the variance computation.

=item B<_OVB::import()>

This module also inherits all the overloads and methods from
L<Statistics::Basic::_OneVectorBase>.

=back

=head1 AUTHOR

Paul Miller C<< <jettero@cpan.org> >>

I am using this software in my own projects...  If you find bugs, please
please please let me know. :) Actually, let me know if you find it handy at
all.  Half the fun of releasing this stuff is knowing that people use it.

=head1 OVERLOADS

This object is overloaded.  It tries to return an appropriate string for the
calculation or the value of the computation in numeric context.

In boolean context, this object is always true (even when empty).

=head1 COPYRIGHT

Copyright 2012 Paul Miller -- Licensed under the LGPL

=head1 SEE ALSO

perl(1), L<Statistics::Basic>, L<Statistics::Basic::_OneVectorBase>, L<Statistics::Basic::Vector>

=cut
