小女子新人报道，望高手相助。
我用VBA写了二叉树期权定价的程序，明明都有按照案例来写，公式也都对的，可是无法运行。
显示总是错误溢出
各位高人能不能帮我看看哪里出问题了。
万分感激，标红的是VBA显示错误的语句。


Function BinoptVal(iopt, iea, S, X, r, tyr, sigma, nstep)
'Returns Binomial Option Value(ipot=1 for call,-1for put;
'iea=1 for euro,=2 for amer)

Dim delt, erdt, u, d, P, pstar, mu
Dim i As Integer, j As Integer
Dim vvec As Variant    'to be a vector
ReDim vvec(nstep)     'know size of vector

'caculate parameters
delt = tyr / nstep  'length of the time step
erdt = Exp(r * delt) 'compounding factor
mu = 0 'the stock growth rate
u = Exp(mu * delt + sigma * Sqr(delt)) 'up multiplier
d = Exp(mu * delt - sigma * Sqr(delt)) 'down multiplier
P = (S * erdt - d) / (u - d) ' up prob
pstar = 1 - P 'down prob

  'calculating vector of option values after n steps
    For i = 0 To nstep
      vvec(i) = Application.Max(iopt * (S * (u ^ i) * (d ^ (nstep - i)) - X), 0)
    Next i
    'calculating conditional payoffs & discounting back step by step
        For j = nstep - 1 To 0 Step -1
            For i = 0 To j
            vvec(i) = (P * vvec(i + 1) + pstar * vvec(i)) / erdt
  Next i
        Next j
   
    BinoptVal = vvec(0)

End Function