Ventana software support forum

Is Lognormal distribution available in Vensim?

I assume you mean with random functions. Just use exp(RANDOM NORMAL(nmean,nstdv,0)). I think, though it is worth double checking, that the mean for this will be

mean of log normal = exp(nmean + nstdv^2/2)

and the variance will be

variance of log normal = exp(2*(nmean + nstdv^2)) - exp(2*stdv + nstdv^2)

Hope that helps.

I wanted to use the suggested formula but I always get a floating point error.
What can be the reason?

Thanks, Danny

most likely your mean and standard deviation put the values out of range. these need to be pretty small numbers since you are passing them through exp. Try with a mean of 0 and a standard deviation of 1.