Ventana software support forum

Hi Bob Effectively, when the lookup tables are out of bounds, it takes the bound of the lookup as value if there is no extrapolate. All the cin files have the same particularities. This does not look very professional for me. The programs look too very difficult to understand, several 1000 loops! no...

Hi I wanted to study the world models that have been translated into Vensim, and found that both models from The 92 or 93 and 2003 when you run them, have lots of out of bounds lookup warnings. The model from the Seventies works all right. It does seem strange that the constants value drive the look...

Hi The best thing to do is to consult the SD organization web site and to browse the archives. There is not much written on pricing generally. I have myself browsed the archives to look about pricing and revenue management. I did not find anything on the subject. There is an explanation about that f...

Hi

You should too put units in your model.
for instance you model has month unit in the settings and you are suppoedl to work in weeks.
Respecting unit is a very easy and unexpensive way to check a model.
there is may be an error that comes from unit inconsistency.
Regards.
JJ

HI About the example that you give using the delay profile I think that the proble comes from the fact that you must give the average delay time plus the profile and Vensim mixes all this to give results that can be a bit surprising. the documentation warns about being careful withe the delay profil...

I tried to download your model example.mdl and it does not work either.
May be a problem with the forum?
Regards.
JJ

Hi

I checked the download and my model was already downoladed several times.
If you cannot donwload, send me your address e-mail, I will
send you the model.
Regards.
JJ

Hi As Bob said, the delay profile should work too, you can choose between both. One thing to consider too is at least at the beginning to work with months instead of weeks, even if it can evoluate to weeks later on. The benefit is to have a simpler model at the beginning that can always be made more...

Hi

Joined a model that uses subscripts that is a bit heavy, but that works.
Regards.

Hi

I did not ask that you show your complete model but one that summarizes the problem.
I have the same problem. I will never show a complete model.
Regards.
JJ

Hi Bob

It is effectively safer to create a constant shut down time and optimize on this constant and on intermediate results instead on a system constant like final time.
Thank you for the advice.
Regards.
JJ

Hi

You should work on making a simple model that resumes your full problem and join the right explanations with it to make your problem understandable to anybody wanting to help you and of course make the model and the documentation available.
Regards.
JJ

Hi

Is is possible to use without problems the final time as a parameter to optimize with other parameters without any difficult to observe side effects. Is seems to work, but I am not absolutely sure of it.
Regards.
JJ

Hi

Here is joined an example of what could be done.
Regards.
JJ

Hi

Here is a model joined that does the job
regards.
JJ

Hi Howard

I still do not undesrstand quite how you want to depict the concurrency. It would eventually be better if you represent somehow the demand.
Regards.
JJ

Hi Joined a model where I have implemented Bob's solution that works well in term of keeping the average of %xfinished randomize close to the %xfinished. I have joined two other options, both with Random uniform, one with the time, that work already fine, the random uniform a little less than the No...

Hi I join a model that brings noise to the percentage of work finished. The problem is that bringing noise to a ratio that must be between 0 and 1 is not easy. Even if you do it, the noise introduces a bias that is measured by accumulating both values, biased and unbiased. I do not know how to corre...

Hi In the third remark, I wrote about one parameter, in fact it must have the lookup table as parameter and the boundaries, plus the stretch and the slide. If you want to introduce some noise using a lookup function, it is better to use a lookup with a distribution choosen by you, and use the result...

Hi I still do not understand what you want to do. But one can make several remarks about your model. First to avoid an error unit, it is better to define a constant for the initial value of x and to use it for the determination of %x finished. Secondly you define the variable Random lookup as a look...

Hi A model is more robust if the risk of its results being far from reality is minimal. The difference of Sterman's approach and SSM relatively to the results will depend on the problem, the ressources allocated to the building of the model: competence of the modeller, time to build the model, quali...

Hi

You'd better send a simplistic model to explain what you are trying to do. I do not see actually your problem.
regards.
JJ

Hi Addor

Can you join a simplistic model to illustrate your problem?
Regards.
JJ

Hi Skjold

If you have Vensim pro you can try something like the model joined.
Regards.
JJ

Hi

the reason why the first job is generated at time 6, with every runs which is normal, is probably coming from a different random sequence numbers generator between the two versions 5.5 and 5.3.
Regards.
JJ