- array_filter: documentation ( source)
- max: documentation ( source)
<?php
$arr1 = array(5, 3, 9, 11, 6, 15);
$arr2 = array(11, 20, 1, 3, 8);
foreach($arr1 as $x) {
$max = max(array_filter($arr2, function ($y) { return $y < $x; }));
echo $max;
}