PHP to implement the Fibonacci sequence of simple writing _php skills

The Fibonacci sequence is a very common type of sequence, and its mathematical definition is: f0=1,f1=1,fn=f (n-1) +f (n-2) (n>=2,n∈n*). This article uses PHP to simply implement the Fibonacci sequence, the code is very simple and understandable, as follows:

<?php 
$arr [1] = 1;
for ($i = 2; $i < $i + +)
{
    $arr [$i] = $arr [$i-1] + $arr [$i-2];
}
echo Join (",", $arr);//merge array into one string output
?>

Thus, the display output of the Fibonacci sequence of n within 100 fn=f (n-1) +f (n-2) is realized.