Ventana software support forum

Can you give an example of what you want to implement? And if you upload what you've tried, that would help as well. Hi thank you a lot. I'm trying to use Vensim to model a probability of infection with a relation I found in Teunis et alii 2016 "A generalized dose-response relationship for ade...

Hi
is there any PLE for Ventity or the only way is to use a 60 days trial?
All the best.
Lorenzo

Hi
is there any way of implementing an hypergeometric function 1F1 with 3 parameters a, b and c in Vensim PLE Plus obviously through some other functions?
Al the best and many thanks for any suggestion.
Lorenzo

Hi to everybody.
Could you please check the attached model? The variable G produces a Normal distribution rather nicely but I have some doubts about the variable L: it should produce a Lognormal distribuion but its graph looks strange to me.
Any idea?
Thank a lot for any help.
Lorenzo

Hi tomfid one more question. If I use the method you gave me for a varibale, let's call it C, in Vensim I cannot use a Monte Carlo tecnique on C. So if I need to use a MC on C (that I know is lognormally distributed with known mu and sigma) is it possible to use a normal distribution? With which par...

Hi tomfid
thank you a lot... I'll do my best to follow your instructions.
Lorenzo

No, I need a lognormal distribution but the data are (now) on a linear (or raw) scale.
Lorenzo

Hi tomfid sorry to be boring but my collegues changed their mind and decided to work on data on a normal scale and so on a non logaritmic scale. Can I use he formulas you gave me as they are or do I need to get hem modified and, if yes, in which way? Why do you use the values -6 and 6? Is it for con...

Perfect, thanks...
Lorenzo

Hi sorry for the delay... first of all thank you a lot... I have still some doubts... If from a statistical analysis of some data I find that they can be thought as being generated by a lognormal distribution with mean m and standard deviation s but the tool I use provides me only a normal distribut...

You are right, sorry... what about the other issues?
Lorenzo

Hi tomfid thank you for your reply. Can you tell me why your random normal has 6 paramaters whereas the one we can find in Vensim RANDOM NORMAL( {min} , {max} , {mean} , {stdev} , {seed} ) has only five? Moreover if I want to use a lognormal distribution with min, Max, m and S by implementing it wit...

Any handy solution?
Lorenzo

Sorry, I posted the wrong model, check this one. Same name but a small difference in one of the variables.
Lorenzo

PLE Plus for Windows 10. This is the error message I get:
ERROR: Fix floating point errors before entering SyntheSim mode.
ERROR: Floating point error computing - "C/100" - at time = 2.000000.
Trying to save the results anyway
Many thanks.
Lorenzo

Hi
here is the model, many thanks for any suggestion. It may look strange since it does not use any stock but for my purposes it's ok.
Lorenzo

Hi all I tried to use the following relation X = e^N to transform a normal variable N (with mean value m and standard deviation s) in the lognormal variable X with the same parameters but when i run the simulation I get an overflow over X. Any suggestion? Is the procedure correct? 8) Best regards an...

Thank you for your reply. I thought I had to modify the shft paramenter instead... could you be so kind of telling me which are the precise meanings of the shift and stretch parameters? I find the Vensim documentation about these topics rather confusing, to say the less...
Lorenzo

Hi to everybody. If I am not wrong it is possible to use a Weibull distribution to replace a Rayleigh one, not available in Vensim, simply putting the shape parameter at 2 but what about the ather parameters in RANDOM WEIBULL( {min} , {max} , {S} , {shift} , {stretch} , {seed} ) if I want that my di...

The issue is that storage for results is allocated at the time of the first (ordinary) run, so if FINAL TIME is longer than that in a sensitivity instance, they get truncated. As a workaround, you could set things up such that an ordinary simulation is longer than your sensitivity range. You'd stil...

Hi first of all season's greetings to everybody.... then my question: is there any way in Vensim PLE plus to perform a Monte Carlo analysis with a randomized FINAL TIME? I trid to insert the FINAL TIME variable among the others during the Sensitivity Simulation Setup as RANDOM UNIFORM 8 12 with a cu...

Hi When I face such cases, I replace the formula that generates an overflow or underflow, by something else that does not change significantly the behaviour of the model. Example joined. If no overflow is set to 0, the model generates an overflow, if set to 1. the formula is replaced by a fixed val...

It's a numerical problem. For small sigma, your stock dynamics rely on compounding a very small number - on the order of 1e-44 for sigma=1.42. That's the threshold of failure - for sigma=1.41, the initial stock is ~1e-45, and the compounding fails because the inflow is then too small to add a signi...

I think it's an initialization problem. When mu=1, the density function looks OK, but the cumulative distribution never reaches 1. That's because the stock (Gaussian Density) is initialized to 0. But when x=0 (at time=0), the CDF should be greater than 0, because x=0 is already near the peak of the...

I haven't replicated your crash - what parameters cause an fp error? You're likely to have problems any time you take EXP(X) for X > 35, due to overflow, but I think here underflow would be the problem. See http://models.metasd.com/cumulative-normal-distribution/ for an alternate approach. Hi thank...