';
$xml .= change($arr);
return $xml;
}
function change($source) {
$string="";
foreach($source as $k=>$v){
    $string .="<".$k.">"; 
    if(is_array($v) || is_object($v)){
        $string .= change($v);
    }else{ 
        $string .=$v;
    } 
    $string .="";
}
return $string;
}

$arr = array(
'name' => array(
    'a' => 'aa',
    'b' => 'bb'
)
);
$xml = arraytoxml($arr);
echo $xml;

aabb