Ventana software support forum

Yes - you can use SAMPLE IF TRUE, or put the value of X into a stock if you're using PLE and don't have that function.

I dunno ... it seems like it might be possible if you hand edit a custom graph, using the :CONFIDENCE or :SENS-LINES keywords. I've never tried it though. If it works, you might still have a lot of problems with overlapping shading. A histogram might be a better option.

You can google the SD conference proceedings with site:systemdynamics.org inurl:conferences plant growth I didn't see much in a quick look, but a little digging might turn up something. A more general search for "plant growth model" generates lots of hits, but you have to translate from di...

Never mind, I can replicate it. Bug ticketed; might take a little while to sort it out.

In most cases, you can simply ignore the posting of interest at discrete intervals, and use a continuous formulation. You can adjust the simple rate of interest for compounding, though at low rates it makes little difference. If the accounting in your model is critical, you can model the posting of ...

I think you'd need a more advanced version, to have the option of coding the custom graph in text.

I think it ought to be possible to simulate portions of the dynamics in double precision Vensim DSS. The largest double is something like 2^308, so the capacity is there. However, even if it could run, you have a problem, which is the cause of your fp error. You're running for 5000 kalpas with a tim...

Ahh ... that's it. The old version is 32bit and the new is 64 - that's why it didn't get overwritten. I think you could just manually delete the old one.

These are pure pipeline delays, so

y = DELAY FIXED( x, duration, x )

is essentially the same as

y = x(time-duration)

DELAY MATERIAL is the same, except for special treatment to conserve material if the duration increases.

I think that's the limit of the menu, but you should be able to enter a smaller value via the equation editor if desired.

That's odd. I don't think any of the install paths have changed, so all shortcuts should point to the newest version, and the old should be overwritten. The only thing I can think of is to do a control panel uninstall, then manually clean up by deleting any Ventity stuff in \Program Files, then rein...

Time in Vensim is essentially abstract, so the day/month treatment is a modeler choice. A time step of 1/30 (or 1/30/4) months could pose problems with roundoff error - my guess is that's why the modeler chose 1/32/4. Not sure why they didn't just use a time unit of days with a time step of .25 - th...

I wouldn't call it "unrealistic" - if the event really is discrete, then the flow is (asymptotically) infinite. It does look weird though, and can be tricky for an unfamiliar viewer to interpret. An alternative would be to spread the event out over some duration > TIME STEP: inflow rate = ...

CohortPop5+ageMonitorAlt.zip Here's an example. I've added an attribute, "is childbearing age," that contains "yes" or "no". Then I created a collection, cohort[parent population, is childbearing age] that calculates some aggregates, like the population of child bearin...

Selection by value is an unimplemented feature. There are a couple of possible workarounds - I'll test to see which works best.

There aren't any hard limits on size, so your setup should work.

When you want an effectively instantaneous event, the magnitude of the rate needed to accomplish a given change in a level varies with the TIME STEP. You can see why by looking at the Euler step for a level: level(t) = level(t-dt) + rate*dt As dt gets smaller, the rate has to get bigger to compensat...

An auxiliary using itself implies a(t) = f( a(t) ), which is causally nonsensical. a(t) = f( a(t-delta) ) implies a lag or accumulation, which can be implemented with a DELAY function or more commonly a Level variable. If a stock (level) is subject to a min or max constraint, as for a bathtub which ...

How about some kind of simple expression, like: fraction new phones= 0.5 Units: fraction [0,1] max degradation from new phones= 0.2 Units: fraction [0,1] max neutral frac new phones= 0.4 Units: fraction Threshold, beyond which new phones degrade performance relative comm speed= 1-max degradation fro...

This is cool. I think it's also the very first working Ventity model submitted by an external user - a bit of a milestone for us. Thanks! It would be cool to have an infectious disease variant of this, where each cohort is essentially an SIR model, with infection crossover among the cohorts. I'll ha...

This archive contains some examples of cohort models. I explain how they work in a video https://vimeo.com/140356008.

That would be one way to design it, yes. You could also create a conventional aging chain, but I think it's more work without any corresponding improvement in insight.

I'm posting a video and some sample models shortly.

Yes - the text tool seems to be buggy. We'll fix it, but in the meantime avoid it. The yellow sticky note seems fine though.

Strange - I find that both behave identically.

Hi JJ - I'm not entirely sure what you mean by "reachable". In terms of visibility and ability to draw an arrow to X, they seem the same to me. - T