VBA Monte Carlo Simulation - Repair Time Generator (Lognormally Distributed)

Question

my name is Rik and I'm a 6-sigma green belt, and I've created a Monte-Carlo Simulation of an Aircraft Engine repair facility. I'm currently doing a 6-sigma project on in Excel VBA.

I simply scaled a random number while I was developing the program, but now that it's developed I'd like to use the inverse lognormal CDF http://engineer.jpl.nasa.gov/practices/at2.pdf to create the random repair times, but I couldn't find the function online.

I did find the below code on http://www.anthony-vba.kefra.com/vba/vba12.htm but it is for the normal distribution and I'm not certain of it's accuracy. I couldn't find an equation for the inverse lognormal CDF. I'd like similar code for the inverse lognormal CDF function.

Any help is greatly appreciated.

'****************************************************************************
'*         Return random numbers from Standard Normal Distribution          *
'****************************************************************************
Function gauss()
    Dim fac As Double, r As Double, V1 As Double, V2 As Double
10      V1 = 2 * Rnd - 1
        V2 = 2 * Rnd - 1
        r = V1 ^ 2 + V2 ^ 2
        If (r >= 1) Then GoTo 10
        fac = Sqr(-2 * Log(r) / r)
        gauss = V2 * fac
End Function

Answer 1

If you are using Excel VBA the Excel function Loginv together with a random number between 0 and 1 can be used to generate a random Log-normally distributed number.