$3$avec$($grad$)\backslash$times $(\backslash$phi vec$($A$))=($vec$($grad$)\backslash$phi $)\backslash$times vec$($A$)+\backslash$phi $($vec$($grad$)\backslash$times vec$($A$)),$ hence that grad$^(2)($r$^($n$)$vec$($v$^(\text{'})))=$n$($n$+3)$r$^($n$-2)$vec$($r$)$ solve it