How to display a complete diamond in PHP

make-diamond.php

<?php

$n = 9;
$index = 1;
$trend = 'upward';
for ($i=1; $i <= $n; $i++) { 
	$stars = $n - ($n - $index);
	if($index >= $n){
		$trend = 'downward';
	}

	if($trend == 'downward'){
		$index = $index - 2;
	} else {
		$index = $index + 2;
	}

	$spaces = ($n - $stars) / 2;

	for ($j=1; $j <= $spaces ; $j++) { 
		echo '-';
	}

	for ($j=1; $j <= $stars ; $j++) { 
		echo '*';
	}

	for ($j=1; $j <= $spaces ; $j++) { 
		echo '-';
	}
	echo '<br />';
}