I don't know where to put this
"private function _addSitemapNode($fd, $loc, $priority, $change_freq, $last_mod = null)
{
fwrite($fd, '<loc>'.(Configuration::get('PS_REWRITING_SETTINGS') ? '<![CDATA['.$loc.']]>' : $loc).'</loc>'."\r\n".'<priority>'."\r\n".number_format($priority, 1, '.', '').'</priority>'."\r\n".($last_mod ? '<lastmod>'.date('c', strtotime($last_mod)).'</lastmod>' : '')."\r\n".'<changefreq>'.$change_freq.'</changefreq>'."\r\n");
}"
in the file