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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: 4
Views: 16

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: 4
Views: 16

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: 3
Views: 11

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: 18

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: 18

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: 31

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=vector+elm+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: 70

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: 136

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: 136

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: 136

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: 136

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...
by LAUJJL
Thu May 10, 2018 7:11 am
Forum: Vensim
Topic: Discrete Event Probability
Replies: 11
Views: 136

Re: Discrete Event Probability

Hi

Another formulation possible in the model joined.

Regards.

JJ
by LAUJJL
Sun Apr 29, 2018 8:24 am
Forum: Vensim
Topic: longest run of zeros
Replies: 4
Views: 80

Re: longest run of zeros

joined a model to reset a level to 0. Does not use the sample if true, normally not available in PLE plus.
by LAUJJL
Mon Apr 23, 2018 7:57 am
Forum: Vensim
Topic: Subrange of Subrange for Subscript
Replies: 3
Views: 111

Re: Subrange of Subrange for Subscript

Hi

There is no problem with the model I uploaded. The model is intended to eventually answer the question.

Regards.

JJ
by LAUJJL
Sun Apr 22, 2018 6:01 am
Forum: Vensim
Topic: Potential doublecounting in a example model
Replies: 8
Views: 203

Re: Potential doublecounting in a example model

It is possible too to just discard the replacement houses and keep the gap, to avoid double accounting. it genereates a slightly different behaviour, but it does not change it funtamentally.

See joined a corrected model with the three options.

Regards.

JJ
by LAUJJL
Sat Apr 21, 2018 9:25 am
Forum: Vensim
Topic: Subrange of Subrange for Subscript
Replies: 3
Views: 111

Re: Subrange of Subrange for Subscript

Hi

joined a correct example.

Regards.

JJ
by LAUJJL
Fri Apr 20, 2018 3:05 pm
Forum: Vensim
Topic: Potential doublecounting in a example model
Replies: 8
Views: 203

Re: Potential doublecounting in a example model

Hi Wayne Not being a professional of that job, it is difficult to be categorical. The demolished houses having no delay, one can add a smoothing action, with what period? Adding another smooth to the gap, seems a bit a lot, as there is already a time to respond to gap, which is already a smoothing a...
by LAUJJL
Thu Apr 19, 2018 5:56 pm
Forum: Vensim
Topic: Potential doublecounting in a example model
Replies: 8
Views: 203

Re: Potential doublecounting in a example model

Hi I had too noticed that. But I considered that both solutions can be right. If one considers only the gap, of course one must take away the replacement houses. But one can too consider that taken into account the time to respond to gap, houses demolished will enter more quickly the planning and ta...
by LAUJJL
Thu Apr 12, 2018 7:02 am
Forum: Vensim
Topic: lookup table
Replies: 16
Views: 244

Re: lookup table

Hi Here is the model corrected, with a unit correction (the model has strictest unit testing set on) and the initial GDP set outside the GDP equation (best practice). the llokup now starts from year 1 (2017) to year 2 (2018. The model is in published format (vpm) downloadable with any Vensim version...
by LAUJJL
Wed Apr 11, 2018 6:49 pm
Forum: Vensim
Topic: lookup table
Replies: 16
Views: 244

Re: lookup table

Making a variable time dependant, is like inputing this variable as an external data.
by LAUJJL
Wed Apr 11, 2018 5:13 pm
Forum: Vensim
Topic: lookup table
Replies: 16
Views: 244

Re: lookup table

Hi Tom Your équations are mathematically correct (see model joined) but I was saying that a growth rate depending on time was economically not very realistic. The growth rate is realistically more a constant like an interest rate , one of the run joined than growing linearly like the second run join...
by LAUJJL
Wed Apr 11, 2018 3:20 pm
Forum: Vensim
Topic: lookup table
Replies: 16
Views: 244

Re: lookup table

Hi

A growth rate that dépends on time, looks Strange.

generally the growth rate dépends on the level, like a bank account with interests.

Regards.

JJ
by LAUJJL
Mon Apr 09, 2018 9:48 pm
Forum: Vensim
Topic: Vensim PLE INTEG UNABLE TO UNDERSTAND RIGHT HAND SIDE OF EQUATION
Replies: 2
Views: 104

Re: Vensim PLE INTEG UNABLE TO UNDERSTAND RIGHT HAND SIDE OF EQUATION

Hi

A bug in the previous model, where I do not take into account the inertia of the stock of salesman.

Corrected with this model joined.

Regards.

JJ
by LAUJJL
Mon Apr 09, 2018 7:02 pm
Forum: Vensim
Topic: Vensim PLE INTEG UNABLE TO UNDERSTAND RIGHT HAND SIDE OF EQUATION
Replies: 2
Views: 104

Re: Vensim PLE INTEG UNABLE TO UNDERSTAND RIGHT HAND SIDE OF EQUATION

Hi

the level is missing an intial value and does not need an integ twice.

See the model corrected with some small added variables and some graphs to be used with the synthesim.

Regards.

JJ
by LAUJJL
Fri Apr 06, 2018 1:12 pm
Forum: Vensim
Topic: Can I take in input data paths from another input data file?
Replies: 12
Views: 527

Re: Can I take in input data paths from another input data file?

Hi in fact there are two problems with strings in Vensim. First, a string cannot never been equal to a formula. It can only be equal to a string constant surrounded with quotes. It is then impossible to change its value based for instance on another numeric value. The second problem is that it seems...

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