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Hmm ... sounds like a server MIME type issue. Shouldn't happen with the .vpm version. The .mdl works fine for me in Firefox - what browser are you using?

No. What version of Vensim are you using. Did you try the .vpm version?

It might be worth trying the 2010 version. I know Bob had to skip a couple of versions of visual studio because he couldn't get Vensim to compile properly.

Tom

One more thought: maybe there's a way on the Excel side to make the workbook less obtrusive. One common issue, for example, is Excel's frequent request to recalculate spreadsheets that are saved in older versions; updating might help. It also might be possible to write a VB script that would minimiz...

You can always build a separate submodel of your SIMULTANEOUS equations, where time represents each iteration of the SIMULTANEOUS loop, so that you can test what's going on internally.

Tom

I assume you're using the GET XLS functions? In that case Excel does need to launch. As an alternative, you can put constants and data in input files, so no Excel is needed. For constants, see ".csv files using to input changes" and "Constant Input Files" in the online help index...

Bear in mind that any calculation of derivatives or trends over short times (like TIME STEP) will be very sensitive to noise or discontinuities. If you're modeling a real-world decision, there has to be significant smoothing (which implies delay) in the trend perception process.

Tom

Hi -

I just posted a new set of DICE versions here
http://models.metasd.com/2010/06/dice/

Tom

Why not paste directly from Vensim into the Powerpoint presentation? That would preserve the vector graphics.

Got it ... That's an easier problem, I think. One option would be to develop a common interface in something like Java, C, or Excel/VB and use that to run both models. For Vensim that's easy, using the .dll (see the examples that install with the Vensim app in vensim\dll). I don't know how it would ...

When you say "integrate" do you mean run the same model in Vensim and GAMS, for comparison, or run the two in sequence to solve different parts of a problem, or ... ? For comparison/replication, the basic challenge is to translate the GAMS model into differential equations; then it's easy ...

There are many applications in engineering project management and management science. Are you looking for things on the boundary of engineering, or actual engineering tasks (modeling physical devices etc.)? You might also ask about system dynamics engineering applications at the SD forum, http://www...

It's available electronically under the help menu.

With a 3min service time, a teller could serve 20 customers/hour, so you could set the service rate to 20. That would correspond with an exponentially distributed service time with a 3min mean. However, the actual throughput will be somewhat different, due to occasional waiting. You could set INITIA...

After some further reflection, I think my model is correct as a representation of a queue with Poisson arrivals and exponentially distributed service time. I implemented some of the analytic results for an M/M/1 queue, and the results conform to that, though I only checked two cases, and not with la...

JJ - Thinking some more, I guess one reason for the difference between models is that your DELAY MATERIAL effectively has a deterministic service time? I looked at the 1hr residence times with the Poisson distribution - they seem unlucky, but at the 1% probability level, and therefore not totally cr...

One possibility is that something else is locking files on your system. Do you use Groove or Dropbox or some other directory sharing? One thing that might help is to set a backup directory (Tools>Options>Startup; mine is C:\Program Files\Vensim\backup ). That keeps your model directories free of ext...

I haven't had a chance to look into it further, but I think in part "right" depends on what you think the actual behavior of the teller service time is. Could it be exponentially distributed? Or is it more consistent (lower variance) than that?

I haven't had a chance to look at your models yet, but it occurs to me that you would expect the average cycle time to be different from the service time (1/mean service rate), because the total cycle time includes both the time it takes to be serviced AND any time waiting in the service queue. (How...

JJ - I haven't had a chance to look at the model again, but here are a few quick comments: - The effective distribution isn't quite Poisson, because the maximum exit rate is truncated by the size of the queue. - I hardly thought about the distribution, just trying to get the model running with integ...

.vgd format is for custom graphs, which you can load via SPECIAL>READCUSTOM (but you don't normally need to do this if your custom graphs are in your model file).

LOADMODEL takes a model in .mdl, vmf, vpm, or vpa format (see the online help, DSS reference supplement, chapter 5).

"xxx is not used in the model" messages are just a warning; they might help you find a variable that is unused, but should be. For a reporting variable like the average arrival rate, that you don't intend to use, you can suppress the warning by checking the "supplemental" box in ...

Here's another version of the model that handles the Poisson arrivals/departures as discrete events. One thing to note is that in the original model, the TIME STEP (0.5) was too short given the service time (0.05) - if a queue or level is modeled explicitly, the time step needs to be shorter than th...

Actually you want the .vpm version that I posted here, http://models.metasd.com/2010/04/rental ... -dynamics/

You can run it with the free Vensim Model Reader, which handles things that PLE won't (arrays, advanced functions, ...)

Tom

You might take a look at the handling of the discrete arrivals in the carRental.mdl model in this thread:
http://www.ventanasystems.co.uk/forum/v ... php?t=4076

Tom