Ventana software support forum

Krishna, apologies; attached is the revised model, I forgot to add an important non-negativity constraint to the outflows of the common resources.

Best.

Karan

Hi Krishna, Attached is the model as you would need it - you can change the parameters. In the same fashion as JJ, I have not used allocation by priority. The "prioritization" takes places by using a condition that once the additional demand of A is met, the flow for additional material fo...

Very good advice. I had in fact "fitted" the curve (for the actual problem the data is s shaped) and optimized the co-effecients but I thought it would be good to learn how to use the lookup - again, as always, thanks for your time JJ!

aha! Thanks JJ!

Best Wishes,

Karan

Greetings! Please see model attached. I use "time" to get values from an array, "investment profile," into the variable "investment". 1) The value of "investment" is slightly different from that of the values in the "investment profile" array; since ...

Thanks Bob - will keep you posted!

Glad to see this in the recent 5.9e update. Seems pretty solid so far - a few notes: - Certain files (for example all the .mdl files supplied in the Business Dynamics CD) do not open. - The equation editor needs a little bit of space, perhaps a few pixels worth, on the left hand side of the window (...

It most likely means "a function of": "the effect of academic staff quality on university reputation is a ratio of current to historical perceived academic staff quality"

Thanks! For now, this works!

Greetings! Attached is an excel file and the beginnings of a dynamic model of a company's P&L statement. The Get XLS command will read values "time down". On some columns for example "o13" or "l13" Vensim imports the data correctly; however, on other columns such as...

Sales Force will have units {people} net hiring rate will have units {people/year} or {people/month} In order for there to be exponential growth, the rate of growth i.e "net hiring rate" must be proportional to the current number of people in the "Sale Force" stock. You define a ...

Is there a vensim function to take derivatives automatically; or do I have to create a new variable which calculates the difference between the variable of interest at the current time step and the previous and then divides it by dt: dV/dt = (V(n)-V(n-1))/dt then repeat similarly to calculate the se...

Thanks Bob, that's quite useful!

I'd presume that you'd have to:
1) build age-specific cohorts for each of the two genders [see Business Dynamics Chapter 12];
2) run your model;
3) export the raw data into excel;
4) create a graph for the simulation results at the time in question.

Best

Karan

Hi JJ, there is a meeting on issues related to Sustainable Development organized by the Balaton Group next month (September '09). I was just wondering if there are any other forum members attending.

Best Wishes,

Karan

One way to prevent negative stocks is to use MIN and MAX functions in the following way: For Inflow (IR): IR = MAX(0, Desired Inflow), where Desired Inflow could be whatever. This way if Desired Inflow is negative the flow constrains it self to 0. For Outfow (OR): OR = MIN(Maximum Outflow, Desired O...

Dear JJ

Thanks for the clarification!

Best

Karan

This was a useful discussion. Thank you!

JJ you mentioned that you " solve the problem of continuity by setting a penalty equation that is both continuous and has a left and right derivative" Could you elaborate, or give us an example?

Best Wishes,

Karan

Anyone attending the meetings in Balaton this coming September?

Best Wishes,

Karan

Problem Solved: I am running Vensim via Windows XP in Parallels on OS X. For some reason I can only load and save files in DSS from the root directory of the XP virtual drive; this means that Parallels Desktop won't allow Vensim DSS to modify files on the OS X desktop. Best Wishes, Karan [Edited on ...

I can't save either I get the message "Bad Directory\.psf\Home\Desktop\.psf\Home\Desktop\."

Dear Tony, Bob,

Unfortunately the models do not open in DSS; however, if I open them in PLE PLUS I have no issues. The models were created in PLE PLUS on the same computer, same path.

Perhaps I should remove PLE PLUS?

Best

Karan

Dear Bob,

I am trying to open files in DSS that I created in PLE Plus but I get the following error:"unable to change directory to \.psf\Home\Desktop\.psf\Home\Desktop\."

Any suggestions?

Best Karan

Dear Stephen, Attached is a model which should do what you want. I am using a cascading stock structure similar that of JJ's model. Though I have to say this doesn't seem like a natural process for the systems I have come across in my studies, as per your requirements, the model will perform the fol...

As the system time reaches one time constant, a stock (which has no inflow), empties 63% of its contents. By the second time constant it has emptied another 63% of the remaining contents and by the fifth or six time constant it has dumped almost 100% of its initial contents. With reference to the re...