@dist = map sqrt($x[$_]**2+$y[$_]**2+$z[$_]**2), 0..$#x;


##</code><code>##

@dist = map sqrt(($x[$_]-$x0)**2+($y[$_]-$y0)**2+($z[$_]-$z0)**2), 0..$#x;


##</code><code>##

@indices = sort {$dist[$a]<=>$dist[$b]} 0..$#dist;
@dist = @dist[@indices];
@x = @x[@indices];
@y = @y[@indices];
@z = @z[@indices];
@name = @name[@incides];

##</code><code>##

for my $one (0..$#@dist-1) {
    my $two = $one;
    while (++$two < @dist && $dist[$two]-$dist[$one] <= $cutoff) {
        print "found pair: ($x[$one],$y[$one],$z[$one]) and
($x[$two],$y[$two],$z[$two])\n"
            if sqrt(($x[$one]-$x[$two])**2+($y[$one]-$y[$two])**2+($z[$one]-$z[$two])**2) <= $cutoff;
    }
}