function largest_palindrome($text)
{
$begin = explode(" ",microtime());
$matrix = array();

// build match matrix.
// Note: matrix[i][j] is COLUMN i, ROW j.

for ($i = 0; $i < strlen($text); $i++) // each column
{
$matrix[$i] = array();
for ($j = 0; $j <= $i; $j++) // each cell down to the diagonal
$matrix[$i][$j] = $text[$i]==$text[$j] ? ($j<$i ? 2 : 1) : 0;
}

// Go through each column from right to left
for ($i = strlen($text)-1; $i >= 0; $i--)
{
// Go through each cell down to the diagonal
for ($j = 0; $j <= $i; $j++)
{
$max = 0;
// Find the maximum in the horizontal row above and to the right
for ($k = $i+1; $k < strlen($text); $k++)
$max = max($max, $matrix[$k][$j-1]);
// Find the maximum in the vertical row above and to the right
for ($k = 0; $k < $j; $k++)
$max = max($max, $matrix[$i+1][$k]);
// Add this maximum to the current cell.
$matrix[$i][$j] += $max;
}
}

$max = 0;
// Find largest value in the matrix
foreach ($matrix as $column)
foreach ($column as $cell)
$max = max($max, $cell);
$end = explode(" ", microtime());
print "Calculated result in ". ($end[0]+$end[1]-$begin[0]-$begin[1]) ."seconds \n";
return $max;
}