Ventana software support forum

Hi Bob I agree completely with you about the necessary scientific mentality needed, that I would name highly exacting and not suffering the least impasse. The economic and business world doest not work that way. For this reason I do not think that there is a quick solution to the adoption of SD at l...

Hi Bob Thank you for your answer. I ask that question in relation with the last trend on the SD mailing list, because I am convinced that the real reason of the slow increase of SD, is in fact that the end users that have tried SD have had more bad experiences than good ones. Companies are able to m...

Hi I do not remember having once seen any Vensim model in the litterature, for instance those published at the SD annual conference, using explicitely reality checks. Reality checks are not used in the Sterman's book because this feature is no implemented in the two other softwares. I am asking two ...

Hi The utility of modelling is generally not to give precise results but to help better understand the problem at hand. This understanding comes gradually and it is to my opinion better to build very simple models first and use them extensively to get a feel of the problem. I think it is much more d...

Hi Nik Using subscripts is not straightforward and needs practice. You must learn especially how to use the mapping techniques and the vector elm map function. One good idea would be to simplify your model to the point where you can draw a parallel with it and reality even if the reality is highly a...

Hi I have modified my first post, because I used time steps instead of stages. Another reflexion about your model, is : did you test your model against past data? Briefly, is your model a product of your imagination, experience without having been tested with past data, or does its results stand too...

Hi About the simultaneous error there are several ways to solve the problem. You must first study the chain of causal loops, and determine if effectively variable1 influences variable2 that influences variable 3 etc... that influences back variable 1 IN THE SAME TIME STEP. If it is the case, then it...

Hi The fist way to simplify your model is to use subscripts. It looks awfully complicated without it. A second reflexion is why you feel necessary to use 25 stages through a 25 years carreer? Why not simplify your model and take only 5 or 4 stages? A third way to simplify your model is to take away ...

Hi Nik You should too use subscripts to simplify the presentation of your model. At this stage, this kind of model is extremely difficult to manage and using subscripts will considerably ease the writing of the equations and help to understand the model. I hope that you have at least the pro version...

Hi Nik It would be a good idea, if you want some help, to first simplify you problem to the utmost possible to deliver a highly simplified model, (no errors with both C and U checkings) and with full explanation of every variable and every equation. That simplified model does not need to represent y...

Hi Nik As a general rule, I think that you will get better answers to your questions, if you deliver simpler models and with all the checks working correctly. It is easier to understand a model completely checked, espececially units check. It should be simplified to its minimum possible, so as to sp...

Hi Malli The best thing to my opinion is to ignore theory and show concrete examples, starting with simplistic examples and gradually increasing the material of the model, verifying at each step that the person has fully understood what you try to teach. To verify that somebody has understood, he mu...

Hi

Joined a model where you have every time steps, a set of variables generated randomly but can be loaded from real data, and that calculates each time step, the mean and the standard deviation of the set of variables. Vensim pro needed.
Regards.
Jean-Jacques Laublé

joined I hope the model
Regards.
JJ

hi The solution is to try Vensim or to explain closely what kind of problems you are trying to solve. Probably both have their advantages and drawbacks, I do not know simulink, but do you have reality checks implemented in simulink? Serions modeling without such a tool seems difficult to me. You mus...

Look at the world model 2003, that is with the model samples. The time is very much used, and instead of using the time step, they use the variable one year that is equal to the time step. They could have used time stem instead of one year. I think that it is for a reason of lisibility. Studying the...

the model attached may eventually do.
Regards.
JJ

Hi

It is not clear for me.
Logically the way you explain it, there should be only one'1 for output 3.
Regards.
JJ

Study the user guide and in very model explaned, check the units for every equations and try to understand them.
Regards.
JJ

I studied too the nephron model that deals with the find zero and the corresponding nearly identical model with the simultaneous. You do not need to study the whole model to understand how it works, but only the two equations involved! I was first upset too considering the necessity to study the who...

In the first equation, I replaced the initial values that you put in your model by constants, so as to be able to give the constant a dimension, for instance days. Vensim supposes if you use a value in an equation that it is dimensionless and may eventually report a dimension error. So the result of...

Two examples of the forecast. Your model works correctly, excepted units error.
Zipped with winzip
regards.
JJ

Hi Peter What is the ex2 model representing. Three variables: the price that influences positively the supply and negatively the demand. The variable should not be called variable but constant. Is is badly named. sorry. So these variables interact and adjust on each other, until an equilibrium is re...

Hi Peter

Do you understand after my examples, why you model
find zero incomplete cannot work, and stops after the first causal calculation, calculating first x then Z then zero that takes the init value, then stops?
Regards.
JJ

Another more appropriate model, deals with the time step and not the time delivery is the model 3 joined.
You should study the Vensim\models\guide\chapter3, where you find inventory models.
You can find too plenty of inventory in other models too.
Regards.
JJ