my $max = [ $x[ 0 ], $y[ 0 ] ];
for my $i ( 1..$#x ) {
  last if $y[ $i ] <= $max[ 1 ];
  $max = [ $x[ $i ], $y[ $i ] ];
}
print "max at ($max->[ 0 ], $max->[ 1 ])\n";