Código de PHP - Pirámide inversa con letras

<?php

function pyramid($n)

{

    // outer loop to handle number

    // of rows n in this case

    for ($i = $n; $i >= 1; $i--)

    {

        // inner loop to create

        // right triangle gaps on

        // left side of pyramid

        for ($gap = $n - 1; $gap >= $i; $gap--)

        {

            echo"  ";

        }

        // initializing value corresponding

        // to 'A' ASCII value is 65

        $num = 65;

        // loop to print characters on

        // left side of pyramid

        for ($j = 1; $j <= $i; $j++)

        {

            echo chr($num++)." ";

        }

        // loop to print characters on

        // right side of pyramid

        for ($j = $i - 1; $j >= 0; $j--)

        {

            echo chr(--$num)." ";

        }

        echo"\n";

    }

}

$n = 9;

pyramid($n);