Search found 1214 matches

by LAUJJL
Sun Jul 15, 2018 8:07 am
Forum: Vensim
Topic: Subscript error
Replies: 6
Views: 82

Re: Subscript error

Hi

Did you try doing the modifications directly on the text model?

I have experienced some problems using the equation editor for the subscripts and working directly on the text équations is OK.

Regards.

JJ
by LAUJJL
Wed Jul 04, 2018 4:14 pm
Forum: Vensim
Topic: order of calculation of subscripts
Replies: 6
Views: 97

Re: order of calculation of subscripts

Hi

thank you for your answers.

Regards.

JJ
by LAUJJL
Wed Jul 04, 2018 10:05 am
Forum: Vensim
Topic: order of calculation of subscripts
Replies: 6
Views: 97

Re: order of calculation of subscripts

Hi The subscript represents time. I need this to calculate optimal policies each time period, using dynamic programming methods starting most of the time in the past (infinite horizon or not) and going backwards to the present. When one uses traditionnal mapping going from the past, if the number of...
by LAUJJL
Wed Jul 04, 2018 8:23 am
Forum: Vensim
Topic: order of calculation of subscripts
Replies: 6
Views: 97

Re: order of calculation of subscripts

Hi

This solution works if the subscript size is limited, although entering 100 individual equations is rather cumbersome, but if you have a subscript period: (p1-p1000) it is not tractable, especially if you want to modify the size of the subscript.

Regards.

JJ
by LAUJJL
Wed Jul 04, 2018 7:43 am
Forum: Vensim
Topic: order of calculation of subscripts
Replies: 6
Views: 97

order of calculation of subscripts

Hi

When you have a suscript like say period: (p1-p100) and vensim has to calculate for instance the variable var[period] it starts to calculate p1 then p2 etc…
Is there anyway to make Vensim calculate backwards p100 then p99 etc…

Regards.

JJ
by LAUJJL
Wed Jun 20, 2018 6:19 pm
Forum: Vensim
Topic: Single precision problem in Vensim PLE Plus?
Replies: 8
Views: 356

Re: Single precision problem in Vensim PLE Plus?

Hi It does not look like a problem of precision. I have joined the model with an intialization of the level to 100000. Whatever the format of the table, pretty or scientific and whatever its precision, the value for the level is not printed correctly, already at the beginning. If the value of the st...
by LAUJJL
Mon Jun 18, 2018 4:27 pm
Forum: Vensim
Topic: Single precision problem in Vensim PLE Plus?
Replies: 8
Views: 356

Re: Single precision problem in Vensim PLE Plus?

Hi

The level goes very quicky to 100000, in simple PLE and in Vensim DSS simple precision event starting the level at a 0 value!

I do not see where is the problem.

JJ
by LAUJJL
Thu Jun 14, 2018 3:09 pm
Forum: Vensim
Topic: Model Validation
Replies: 14
Views: 534

Re: Model Validation

there are already three tables in the model that show the behaviours of all the variables. You can generally add common or custom tables using the input/ouput oject. if you want to build custom tables you must go to the control panel and graphs and then build a custom table. You can too modify the e...
by LAUJJL
Thu Jun 14, 2018 2:28 pm
Forum: Vensim
Topic: Model Validation
Replies: 14
Views: 534

Re: Model Validation

Hi Sara I do not know which boxes you are talking about. I have joined a second model, where the constants have a lower and upper bound and with sliders. If you run the synthesim in Vensim PLE, you will be able to slide the sliders between their bounds and you will see the values in the tables on th...
by LAUJJL
Thu Jun 14, 2018 9:25 am
Forum: Vensim
Topic: Model Validation
Replies: 14
Views: 534

Re: Model Validation

Hi Sara There is another way to verify a model. It is to verify step by step all the variables calculated, starting by the beginning of what the program calculates. See the order of calculation in the vensim documentation, but it is rather evident. It starts by initializing the levels and then looks...
by LAUJJL
Wed Jun 13, 2018 4:59 pm
Forum: Vensim
Topic: Model Validation
Replies: 14
Views: 534

Re: Model Validation

Hi Sara Anybody wanting to build correct models, is concerned with model validation. There are many papers mainly academic on that subject with structural testing, behaviour testing etc.. Vensim has a special feature called reality check to test models too. The paradox is that if you study public mo...
by LAUJJL
Wed Jun 13, 2018 8:27 am
Forum: Vensim
Topic: Model Validation
Replies: 14
Views: 534

Re: Model Validation

Are you working on real problems and on models that are intended to be used, or in an academic setting?
by LAUJJL
Mon May 28, 2018 8:19 am
Forum: Vensim
Topic: Frechet distribution
Replies: 6
Views: 217

Re: Frechet distribution

Hi lorenzo. When one uses analytical formulations, one is often faced with lack of extreme conditions applicability. There are several ways to deal with these problems. The first one is to replace the analytical formulation by a lookup function, that is more correct but less practical, especially if...
by LAUJJL
Sat May 26, 2018 8:40 am
Forum: System Dynamics Discussion
Topic: requesting resources to understand the mathematics behind system dynamics models
Replies: 5
Views: 456

Re: requesting resources to understand the mathematics behind system dynamics models

Look at the Vensim reference guide, mathematical foundation, especially computational sequence.

Regards.

JJ
by LAUJJL
Sat May 26, 2018 6:10 am
Forum: System Dynamics Discussion
Topic: requesting resources to understand the mathematics behind system dynamics models
Replies: 5
Views: 456

Re: requesting resources to understand the mathematics behind system dynamics models

Hi Arman I think that you may over estimate the capacity of mathematics to explain certain reality. If it was the case, SD would be useless. If you understand intuitively a model, this is enough, and I do not see the utility to add a mathematical explanation. Anyhow when the model gets more complica...
by LAUJJL
Fri May 25, 2018 5:30 pm
Forum: System Dynamics Discussion
Topic: requesting resources to understand the mathematics behind system dynamics models
Replies: 5
Views: 456

Re: requesting resources to understand the mathematics behind system dynamics models

Hi

The need of mathematics is extremely variable, depending on what you are doing with SD.

What do you do with SD?

Regards.

JJ
by LAUJJL
Fri May 25, 2018 5:08 pm
Forum: Vensim
Topic: Frechet distribution
Replies: 6
Views: 217

Re: Frechet distribution

Hi

If you type Fréchet distribution in google, Wikipédia explains how to get a Fréchet distribution from the uniform (0,1) distribution.

Regards.

JJ
by LAUJJL
Fri May 25, 2018 4:57 pm
Forum: Vensim
Topic: Forward-looking expectations in Vensim
Replies: 3
Views: 165

Re: Forward-looking expectations in Vensim

Hi An expectation is always different from what happens. If the expectation changes every time period, one should think about how the expectation is built and shat is expected. for instance what is the horizon of the expectation. What is influencing the expectation? Generally it is one or more level...
by LAUJJL
Fri May 25, 2018 2:08 pm
Forum: Vensim
Topic: Forward-looking expectations in Vensim
Replies: 3
Views: 165

Re: Forward-looking expectations in Vensim

Hi

Your explanation needs some précisions.


Joined a simplistic model that can be taken as a starting point.

Regards.

JJ
by LAUJJL
Tue May 22, 2018 6:16 am
Forum: Vensim
Topic: VECTOR ELM MAP - how to avoid error messages and set NA to 0?
Replies: 5
Views: 177

Re: VECTOR ELM MAP - how to avoid error messages and set NA to 0?

Hi

go to

viewtopic.php?f=2&t=3192&p=22055&hilit= ... map#p22055


it will ho to avoid using the tricky and Dangerous vector elm map function.


Regards.

JJ
by LAUJJL
Thu May 17, 2018 4:01 pm
Forum: Vensim
Topic: Model CDF without a closed-form solution
Replies: 8
Views: 218

Re: Model CDF without a closed-form solution

Hi

A lookup is not fixed and you can vary it using the vector lookup formula.

See the model joined.

Regards.

JJ
by LAUJJL
Sun May 13, 2018 10:07 am
Forum: Vensim
Topic: Discrete Event Probability
Replies: 11
Views: 352

Re: Discrete Event Probability

Hi Tom I am presently studying Dynamic Programming to integrate it to my models. It looks until now that Vensim is totally adapted to this method, which is good news. It is too a lot of fun, because it seems to increase considerably the adaptability of my models to my problems. In the last book, 'an...
by LAUJJL
Fri May 11, 2018 8:23 am
Forum: Vensim
Topic: Discrete Event Probability
Replies: 11
Views: 352

Re: Discrete Event Probability

Hi Tom Thank you for bothering with this problem. Your solution works well with a small number of states. Even with a small number of states, one still has to optimize, and it is not possible to use the synthesim and optimize at the same time like what one does with the synthesim and the sensibility...
by LAUJJL
Thu May 10, 2018 4:42 pm
Forum: Vensim
Topic: Discrete Event Probability
Replies: 11
Views: 352

Re: Discrete Event Probability

Hi Tom In fact the machine has three possible states and the state at the end of one step depends on the state at the beginning of the step and on the additional cost that will determine the transition probability from one state to another one. Each probability is of course less than 1. I know that ...
by LAUJJL
Thu May 10, 2018 3:26 pm
Forum: Vensim
Topic: Discrete Event Probability
Replies: 11
Views: 352

Re: Discrete Event Probability

Hi Tom The formulation I used is certainly redundant but it shows better that the interval (0, prob a) of length a corresponds to the probability of a, as the interval (prob a, prob a + prob b) of length b corresponds to the probability of b and the interval of (prob a + prob b , prob a + prob b + p...