Fonctions personnalisées et boucles dans vba

Bonjour,

Function AA(Vl As Variant, sigma As Double, mu As Double, datevalo As Date, datecheance As Date) As Variant
Dim pas As Single
Dim delta As Variant
Dim normu As Variant
Dim norsigma As Variant
Dim normsimule As Variant
Dim j As Integer
pas = 7 / 365
delta = (datecheance - datevalo) / 7
normu = (mu - 0.5 * sigma ^ 2) * pas
norsigma = sigma * Sqr(pas)
For j = 1 To delta
Randomize
normsimule = Application.NormSInv(Rand)
Vl = Vl * Exp(normu + normsimule * norsigma)
Next j
AA = Vl
End Function

quelqu'un peut m'expliquer pourquoi ça marche pas !!!
merci d'avance