Ejemplo arrays inputs

<!DOCTYPE html>
<html>
    <head>
        <meta charset="UTF-8">
        <title></title>
    </head>
    <body>
        <?php
        $valor = filter_input(INPUT_GET, "valor", FILTER_DEFAULT, FILTER_REQUIRE_ARRAY);
        print_r($valor);
        ?>
        <form>
            <?php
            for ($i = 0; $i < 3; $i++) {
                for ($j = 0; $j < 3; $j++) {
                    ?>
                    <input type="text" size="3" name="valor[<?= $i ?>][<?= $j ?>]">
                    <?php
                }
                echo "<br>";
            }
            ?><input type="submit">
        </form>
    </body>
</html>