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+package matchers::median;
+
+=head1 NAME
+
+matchers::median - Find persistant change in latency
+
+=head1 OVERVIEW
+
+The idea behind this matcher is to find sustained changes in latency.
+
+The median matcher takes a number of past median latencies. It splits the latencies into
+two groups (old and new) and again finds the median for each groups. If the
+difference between the two medians is bigger than a certain value, it will
+give a match.
+
+=head1 DESCRIPTION
+
+Call the matcher with the following sequence:
+
+ type = matcher
+ pattern =  median(old=>x,new=>y,diff=>z)
+
+This will create a matcher which consumes x+y latency-datapoints, builds the
+two medians and the matches if the difference between the median latency is
+larger than z seconds.
+
+=head1 COPYRIGHT
+
+Copyright (c) 2004 by OETIKER+PARTNER AG. All rights reserved.
+
+=head1 LICENSE
+
+This program is free software; you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation; either version 2 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program; if not, write to the Free Software
+Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+
+=head1 AUTHOR
+
+Tobias Oetiker <tobi@oetiker.ch>
+
+=cut
+
+use strict;
+use base qw(matchers::base);
+use vars qw($VERSION);
+$VERSION = 1.0;
+use Carp;
+
+# how many values does the matcher need to do it's magic
+sub Length($)
+{
+    my $self = shift;
+    return $self->{param}{old} + $self->{param}{new};
+}
+
+sub Desc ($) {
+    croak "Finde changes in median latency";
+}    
+
+sub Test($$)
+{   my $self = shift;
+    my $data = shift; # @{$data->{rtt}} and @{$data->{loss}}
+    my $ac = $self->{param}{old};
+    my $bc = $self->{param}{new};
+    my $cc = $ac +$bc;
+    my $oldm = (sort {$a <=> $b} @{$data->{rtt}}[-$cc..-$bc-1])[int($a/2)];
+    $ac++;
+    my $newm = (sort {$a <=> $b} @{$data->{rtt}}[-$bc..-1])[int($bc/2)];
+    return abs($oldm-$newm) > $self->{param}{diff};
+}