Square Number Diamond Pattern

<?php
/*********************************
FILENAME     : diamond.php
PURPOSE      : print square number in diamond pattern
CREATED DATE : 2012-12-13
CREATED BY   : cahya dsn
**********************************/
function diamond($n=3)
{
  $space=strlen($n*$n)+1;
  for($i=0;$i<$n*2;$i++){
    $rst='';
    if($i<$n){
      for($j=0;$j<=$i;$j++){
        $r=($n*$i+1)-($n-1)*$j;
        $rst.=str_pad($r, $space, " ", STR_PAD_BOTH);
      }
    }else{
      for($j=2*$n-$i-1;$j>0;$j--){
        $r=($j+$i+1)*$n-($n*$n+$j)+1;
        $rst.=str_pad($r, $space, " ", STR_PAD_BOTH);
      }
    }
    echo str_pad($rst, $n*$space, " ", STR_PAD_BOTH)."\n";
  }
}

//example use:
echo "<pre>";
diamond(3);
diamond(6);
diamond(10);
?>