Ventana software support forum

Hi

What about updating the sd mailing list archive that is now more then two months old?
I have unsubscribed from the Sd mailing list because of too much work but still like to have a look at the past discussions.
Regards.
JJ

Hi Ralf I think that the time it takes to get any positive results from SD depends on a lot of factors. Mainly the kind of subject, the expertise of the modellers, the knowledge of the subject from the people dealing with it, the ability of the organisation to implement new methods, the state of the...

Hi

dates are incorrect and need to be changed.
Regards.
JJ

Hi Lean thinking cannot be considered as a paradigm (a scientific or sometimes not so scientific, methodology to explore the world) but the basis of human progress towards more value with less effort that has governed the world since the beginning of humanity. So lean thinking is not new, but has be...

Hi

I do not understand your question.
I think it needs a better formulation.
Regards.
JJ

Hi One way is to build variables subscripted with the dimension of the subscript approximately equal to the number of iterations expected and to make the variables equal to the values of the variables for each iteration. joined a simplistic example that computes the limit of 1 / 2N when N is increas...

there was a mistake in the polarity of one of the arrow
joined the corrected model

second model joined

Hi You can have in the same lookup a positive and a negative influence at the same time. Here is joined two models: one with the loop with nothing in it with a negative and positive lookup, and one with two loops that gives the same result than the first but with the positive and negative loop split...

Hi I use two ways to deal with that problem. One way is just to leave things like they are, and draw a loop with no sign in it, meaning that the loop can be positive or negative. If one wants absolutely to know when the loop is negative or positive the solution is to replace the arrow that can be po...

Hi

joined the right model, the previous was empty.
Regards.

Hi

Here is the forecast equations in a model.
Regards.
JJ

Hi Forecast is the equivalent of FORECAST=input*(1+TRD*horizon) TRD = ZIDZ(input-AV,average time*AV) AV=INTEG((input-AV)/average time,ininput) as explained when you consult the index of forecast in the help. All this works in PLE, and if the zidz does not work it is transformable too in a simple equ...

Hi Here is joined a batch file .bat extension that can be called from the exploitation system and that copies automatically the file.xls that you want to extract data to the standard file that is mentionned in your get xls command in Vensim. you do not need to know the command language, you just mul...

Hi When speaking of details, I was just warning you about the fact that I have generally noticed that the utility is not necessarily growing with model complexity and if so much lower than linearly, and the work to do it is growing exponentially. If one faces this fact, is is often better to stay in...

Hi One eventual possibility is to load all the hollydays in an array, where for instance one subscript would be the year and the other the day of the year, with two arrays one for the leap year and another for a not leap year. I would then be easier to fetch the information you need based on the yea...

Hi Bob Thank you for your reply. I know the formulation that you propose, but it is easier to use mine if you want to switch between a lookup extrapolate and a flat 0 lookup. I have a model with a double subscripted lookup table with 45 elements, and it is simpler to change the formula than to modif...

Hi If you can load correctly the data from excell with the get xls lookup for one year, there is no reason why you could not load it with nested if then else with many years. So if it does not work, your if then else's are not correct. Better to join a simple model and a simple Excel sheet to expose...

Hi I use the lookup slope function (an example is joined in a simplistic model) to force the result of a function lookup (extrapolate or not) to be equal to zero outside of the boundaries of the lookup. It seems to work all right (see the model joined). But I use it in a model with subscripts where ...

Hi Bob

Thank you very much for your prompt reply.
Regards.
JJ

Hi When you export the constants and the lookups of a run to a .cin file, the values of the subscripts are not exported. Or one can keep the model the same and decide to run it with different values for the subscripts, depending for instance on the level of aggregation you work with. I have looked f...

Hi In Sterman's book business dynamic there are some examples how price policy influences positive loops, although the price policy is itself driven by positive loops. I moderate what I said about my preceeding post. The best way to see if one can model or not is to try. It all depends on the contex...

Hi Tom I know some politicians. They are more bothered by their re-election than by anything else. They prefer as you say big models because it can help them influence other people while being sure that these people will not been able to really understand them or see that they are wrong. They cannot...

Hi Bob About the sudden death decrease I think that the life expectency should be modelled as a level, as it is a state. It would then behave more smoothly. The problem would be to value it. About the just medium between a too highly complex and a too simplistic approach, this is the basic of effici...

Hi Bob and Tom Thank you for your answers. In fact, I did not understand why in the year 1940 in the 2003 model, deaths were suddenly dropping 22.5 % in one year and staying at this level the next years. The model introduces a discontinuity at the year 40, eventually coming from the penicillin (?) t...