Search found 3811 matches
- Mon Oct 26, 2015 11:56 pm
- Forum: Ventity
- Topic: about testing Ventity beta release
- Replies: 9
- Views: 14177
Re: about testing Ventity beta release
Thanks for the straightforward feedback. I think the right mindset is that Ventity is only preferred at the moment for problems where you need for one of its core language benefits: - lists with arbitrary dimensionality of the members, as in a marketing mix model where one product has 7 packages, an...
- Mon Oct 26, 2015 11:47 pm
- Forum: Ventity
- Topic: Executable expiration date
- Replies: 1
- Views: 2765
Re: Executable expiration date
There will be a release very shortly to remedy this.
- Thu Oct 22, 2015 2:50 pm
- Forum: Ventity
- Topic: Problem adding columns to builtin dataset editor
- Replies: 4
- Views: 4353
Re: Problem adding columns to builtin dataset editor
My guess is that you added the Pasture attribute after creating the builtin dataset that populates the cows, right? Unfortunately, there's a bug that prevents the dataset from updating to reflect the new attribute. If you create a new builtin dataset, the Pasture column should be included. This'll b...
- Thu Oct 22, 2015 2:45 pm
- Forum: Vensim
- Topic: How to keep the value of a variable at a certain time step.
- Replies: 1
- Views: 1398
Re: How to keep the value of a variable at a certain time st
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.
- Wed Oct 21, 2015 10:36 pm
- Forum: Vensim
- Topic: Sensitivy of 2 or more variables in one graph
- Replies: 2
- Views: 1882
Re: Sensitivy of 2 or more variables in one graph
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.
- Mon Oct 19, 2015 2:27 pm
- Forum: Vensim
- Topic: Plant Growth Modeling Question
- Replies: 8
- Views: 5595
Re: Plant Growth Modeling Question
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...
- Wed Oct 14, 2015 11:35 pm
- Forum: Ventity
- Topic: Problem with copy paste to a new diagram
- Replies: 2
- Views: 3331
Re: Problem with copy paste to a new diagram
Never mind, I can replicate it. Bug ticketed; might take a little while to sort it out.
- Wed Oct 14, 2015 7:17 pm
- Forum: Vensim
- Topic: Sorry, very trivial question… 2nd part
- Replies: 3
- Views: 2546
Re: Sorry, very trivial question… 2nd part
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 ...
- Mon Oct 12, 2015 8:23 pm
- Forum: Vensim
- Topic: Problem in Scaling
- Replies: 4
- Views: 2556
Re: Problem in Scaling
I think you'd need a more advanced version, to have the option of coding the custom graph in text.
- Mon Oct 12, 2015 8:20 pm
- Forum: Vensim
- Topic: Modeling an Extremely Long Delay
- Replies: 15
- Views: 9229
Re: Modeling an Extremely Long Delay
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...
- Fri Oct 09, 2015 1:44 am
- Forum: Ventity
- Topic: Ventity install question - multiple versions
- Replies: 3
- Views: 4260
Re: Ventity install question - multiple versions
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.
- Thu Oct 08, 2015 5:48 pm
- Forum: Vensim
- Topic: Delay Functions
- Replies: 2
- Views: 2909
Re: Delay Functions
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.
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.
- Thu Oct 08, 2015 3:09 pm
- Forum: Vensim
- Topic: Unrealistic Rates for Realistic Level Behavior
- Replies: 17
- Views: 9248
Re: Unrealistic Rates for Realistic Level Behavior
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.
- Thu Oct 08, 2015 3:08 pm
- Forum: Ventity
- Topic: Ventity install question - multiple versions
- Replies: 3
- Views: 4260
Re: Ventity install question - multiple versions
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...
- Wed Oct 07, 2015 3:21 pm
- Forum: Vensim
- Topic: Unrealistic Rates for Realistic Level Behavior
- Replies: 17
- Views: 9248
Re: Unrealistic Rates for Realistic Level Behavior
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...
- Tue Oct 06, 2015 3:50 pm
- Forum: Vensim
- Topic: Unrealistic Rates for Realistic Level Behavior
- Replies: 17
- Views: 9248
Re: Unrealistic Rates for Realistic Level Behavior
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 = ...
- Mon Oct 05, 2015 10:33 pm
- Forum: Ventity
- Topic: cohort modeling examples
- Replies: 21
- Views: 16468
Re: cohort modeling examples
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...
- Mon Oct 05, 2015 4:47 pm
- Forum: Ventity
- Topic: cohort modeling examples
- Replies: 21
- Views: 16468
Re: cohort modeling examples
Selection by value is an unimplemented feature. There are a couple of possible workarounds - I'll test to see which works best.
- Mon Oct 05, 2015 4:38 pm
- Forum: Vensim
- Topic: Trouble exporting sensitivity dataset
- Replies: 2
- Views: 1985
Re: Trouble exporting sensitivity dataset
There aren't any hard limits on size, so your setup should work.
- Mon Oct 05, 2015 4:36 pm
- Forum: Vensim
- Topic: Unrealistic Rates for Realistic Level Behavior
- Replies: 17
- Views: 9248
Re: Unrealistic Rates for Realistic Level Behavior
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...
- Mon Oct 05, 2015 4:30 pm
- Forum: Vensim
- Topic: Why Auxiliary variable could not use itself
- Replies: 5
- Views: 3611
Re: Why Auxiliary variable could not use itself
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 ...
- Fri Sep 25, 2015 3:17 pm
- Forum: Vensim
- Topic: Variable function
- Replies: 3
- Views: 2152
Re: Variable function
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...
- Fri Sep 25, 2015 2:31 pm
- Forum: Ventity
- Topic: cohort modeling examples
- Replies: 21
- Views: 16468
Re: cohort modeling examples
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...
- Thu Sep 24, 2015 8:39 pm
- Forum: Ventity
- Topic: cohort modeling examples
- Replies: 21
- Views: 16468
cohort modeling examples
This archive contains some examples of cohort models. I explain how they work in a video- Thu Sep 24, 2015 8:19 pm
- Forum: Ventity
- Topic: help to understand how Ventity works
- Replies: 5
- Views: 5286
Re: help to understand how Ventity works
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.
I'm posting a video and some sample models shortly.