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            if (!defined($min) || $dist < $min) { $min = $dist }
        }
    }
    $min;
}
is(minlinkage([0..5],[6..11]), 1.1, 'minlinkage');

# distance between clusters, according to complete linkage (maximum linkage)
# Distance is the max distance between any two cluster elementes
sub avglinkage { 
    my ($icluster, $jcluster) = @_;
    my $sum = 0;
    foreach my $i (@$icluster) {
        foreach my $j (@$jcluster) {
            my $dist = dist($i,$j);
            $sum += $dist;
        }
    }
    $sum / (@$icluster * @$jcluster);    
}
ok(avglinkage([0..5],[6..11]) > 5.7361, 'avglinkage');
ok(avglinkage([0..5],[6..11]) < 5.7362, 'avglinkage');


# distance between clusters, according to complete linkage (maximum linkage)
# Distance is the max distance between any two cluster elementes
sub maxlinkage {
    my ($icluster, $jcluster) = @_;
    my $max;
    foreach my $i (@$icluster) {
        foreach my $j (@$jcluster) {
            my $dist = dist($i,$j);
            if (!defined($max) || $dist > $max) { $max = $dist }
        }
    }
    $max;
}
is(maxlinkage([0..5],[6..11]), 19.3, 'maxlinkage');

# single, average (UPGMA), and maximum (complete) linkage
my %dispatch = ('s'=>\&minlinkage,'a'=>\&avglinkage,'m'=>\&maxlinkage);
foreach my $method (keys %dispatch) {
    my $tree = Algorithm::Cluster::treecluster(data=>$matrix,method=>$method);
    # Test that all data is in the tree
    is (scalar(@$matrix) - 1, $tree->length, "tree size ($method)");

    # According to current $method
    my $clusters = $tree->cutthresh($thresh);
    # Tree cointains only internal nodes
    # Num of internal nodes is one less than leaf nodes
    is (scalar(@$clusters) - 1, $tree->length, "num clusters ($method)");

    # Given a cluster id, what data indexes are in it, i.e. reverse map
    my @clustermap;
    for (my $i = 0; $i < @$clusters; $i++) {
        my $cluster = $clusters->[$i];
        push @{$clustermap[$cluster]}, $i;
    }
    
    # For every pair of clusters, 
    # verify that inter-cluster distance (given $method) doesn't exceed $thresh
    for (my $i = 0; $i < @clustermap - 1; $i++) {
        for (my $j = $i+1; $j < @clustermap; $j++) {
            # Dispatch table to call appropriate metric, i.e. minlinkage when 's'            
            my $dist = $dispatch{$method}->($clustermap[$i],$clustermap[$j]);     
            ok $dist > $thresh, 
                sprintf "%5.2f < %5.2f for clusters %2d and %2d ($method)", 
                    $dist, $thresh, $i, $j;
        }
    }
}

done_testing;