printf OUT "%s to %s Distance=%.5f\n",     
        $data[$i][0], $data[$j][0],
        $data[$i][2], $data[$j][2],
        distance(\@coords_i, \@coords_j);

##</code><code>##

return sqrt(($x - $x)**2 + ($y - $y)**2 + ($z - $z)**2);