Ventana software support forum

Thank you Bob. I studied the project models familiar by the literature and - believe me - they all seems not usefull to me because they are too academic. In practice project dynamics follows other rules, at least Integration and self-referential projects. My problem with filling and depleting an sto...

Thanx JJ, your approach looks interesting but it doesn't shows the three fill-and-depletes. I wonder that you ask "why you do not try to replicate exactly what is happening". I'm just trying this, and hence your critic could rather be "why do you try to replicate what's happening in s...

Thank you Tony, your model looks very interesting. I also took subscripts into consideration but decided against it because it is something special to Vensim. What I want do do, JJ? Well I'm building my own project model because the known models by Richardson, Pough, Lyneis, Ford et al. are related ...

I'm looking for a small model that fills and depletes a stock three times one an other, every time a little bit smaller. That means e.g. Fill up to 20 by a constant inflow, deplete it by a first order delay fill up to 10 by a constant inflow, deplete it by a first order delay fill up to 5 by a const...

Yes, sounds logically and simple. My original problem was more complex, and I hoped to use sample if true. But as usual the question becomes trivial if I take it out of the context. (originally I tried to (almost) deplete a stock say three times serially first if it achieved level a, then if it achi...

Ok, I understand that

only_peak = sample if true(f>1, f, 0)

tests if f is bigger than 1. If not, it's 0. Well, have a look on my sample model. After T=20 the condition becomes valid, and for that case sample if true holds its value you said.

So why is only_peak not equal f after T=20?

No, I don't see how (T isn't fix).

Why is

sample if true(f>1, f, 0)

not 0 whenever f is smaller than 1?

I have a simple question to the "sample if true" function. I have a function f that is small almost everywhere but has a big peak at time T, say f = 100 for time=T and else 0.1. So I want to cut the small noise such that only the peak will remain. I thought that I can do this with e.g. onl...

Oh yes, this morning I played around with the optimizer and multiple restart parameters as I have noted that in earlier trials they were set otherwise. Now as I have chosen Powell and multiple restarts on it is working. Thank you. Is it possible that with 5.7 the default parameters have slightly cha...

I used Optimization for several times, and always it worked. Now I get the message:

No optimization, not creating optimize output file
The final payoff is -0.0318305

What I'm doing wrong?

Regards,
Peter

Oops, have I another bug? I run a model and open the data table for a specific parameter. Then I click to "Export windows content" and switch to Excel. After positioning the cursor in a specific cell I press Ctrl-V and get the Excel message: Can't read data - OK If I click to OK I get only...

Thank you, Bob. This helped. After a quick reinstallation the problem disappeared.

I run Vensim 5.6d under Vista Ultimate on a 22" display with a resolution of 1680x1050 pixels and 32bit color. I used already very often lookup functions and manipulated their graph. When I recently tried this I got the message: Screen too small - try a smaller font on the next dialog It doesn'...

I'm working in Zurich, and give lectures for mathematics and management operations at several instututes. Occasionally I'm trying to combine game theory and System Thinking, e.g. when I show connections between non-cooperative game archetypes and the Senge's archetypes. A special field in game theor...

Thanks JJ. Well I only read Sterman's "Business Dynamics", but - well - I will have a closer look to the user guide too. Nevertheless I don't think that "find zero" is a typical SD function. You remember when I asked for modelling of Bellman's approach? You wrote, that you also t...

Thanks, Bob. Yes I studied NEPHRON. It's a pitty that I have to go through the junk of blood pressure etc.

Why is there no "academic" example that solves a polynomial or transcendental equation with a variable that depends explicitly of time? That would be helpful.

Regards,
Peter

Hi JJ. Thaks alot for your patient help. This isn't self-evident especially if I'm such slow in the uptake. Your models ex1 and ex2 confirmed that I was right when I tried to converted the examples in the manual into models a few days ago. You can be sure that I studied the two examples well before ...

Difficulties starts when the equation to be zerod is not in the variable of the Find Zero function. Look on my example that isn't complete. x is any time dependent parameter in a greater context. z is a (nonlienear) equation in x I'm looking for the zero of z in every time step. I miss one more arro...

Sure, dear JJ, it isn't urgent. I'm looking forward to your example. How do you mean "I did not found the example in the Vensim documentation". If you click on "Help/Vensim Manuals/Reference Manual/Functions and Keywords/Functions E-I/FIND ZERO" then you certainly will see the tw...

Thanks, JJ. No, you must not model the Cournot Duopol. Thank you for your very kind offer. But my problem is not to model the Cournot's Duoplo but to understand the "Find Zero" function. I have chosen Cournot's Duoplo only as an exercise for "find zero". If you don't think that t...

Thank you, JJ, for your details. I'm afraid that I was not able to explain you, that my variables don't have dimensions like Euro or Euro/widget. E.g. the market price is a relative price and a fraction of 1. 1 is the prohibitive price and has no dimension. So I had to put dmnl everywhere. Sorry, th...

Ooops, JJ, the variables are dimensionless. The market shares are fractions of the total market that is assumed as 1. The price is a normed price relative to the threshold if there is no supply. What would you pay for a mobile phone if there is no supply at all? 3000 Euro or 5000 Dollars? In my mode...

Yes of course JJ, I tryied to attach a model. Here I retry it and hope it works now. Two diopolists are trying to maximize their benefit. The price depends of the respective market shares and the benefit is "market share * price - market share * production costs". If the benefit is smaler ...

Once I asked about optimization simulation (Bellman or likewise) and you suggested to use the FIND ZERO function. After a break I'm studying this function now. I have no problem to solve equations in x saved in the variable z that is input to the variable x=FIND ZERO(...z...) which is again input to...

You got it correctly. Thanks for the suggestion, it's great!

Peter