<?php $matrix = [ [1, 2, 3], [4, 5, 6], [7, 8, 9], ];
Standard input is empty
array(3) {
[0]=>
array(3) {
[0]=>
int(7)
[1]=>
int(4)
[2]=>
int(1)
}
[1]=>
array(3) {
[0]=>
int(8)
[1]=>
int(5)
[2]=>
int(2)
}
[2]=>
array(3) {
[0]=>
int(9)
[1]=>
int(6)
[2]=>
int(3)
}
}