Search found 3808 matches
- Fri Jul 28, 2023 9:46 pm
- Forum: Vensim
- Topic: Units Check whack-a-mole
- Replies: 9
- Views: 1142
Re: Units Check whack-a-mole
A stock equation is the integral of a flow over time, so the stock unit has the flow unit * time unit. This is easier to see if you write the discrete update that happens with Euler integration: stock(t+dt) = stock(t) + dt*(inflows-outflows) were t=time, dt=TIME STEP in Vensim. This has units: stock...
- Fri Jul 28, 2023 9:19 pm
- Forum: Vensim
- Topic: Input Mode
- Replies: 2
- Views: 448
Re: Input Mode
I'm not sure what you mean by "input mode".
The conventional way to implement exponential growth is:
stock = INTEG( - outflow, initial stock ) ~ stuff
outflow = stock * loss rate ~ stuff/time
or
outflow = stock / lifetime
The conventional way to implement exponential growth is:
stock = INTEG( - outflow, initial stock ) ~ stuff
outflow = stock * loss rate ~ stuff/time
or
outflow = stock / lifetime
- Fri Jul 28, 2023 9:19 pm
- Forum: Vensim
- Topic: Input Mode
- Replies: 2
- Views: 448
Re: Input Mode
I'm not sure what you mean by "input mode".
The conventional way to implement exponential growth is:
stock = INTEG( - outflow, initial stock ) ~ stuff
outflow = stock * loss rate ~ stuff/time
or
outflow = stock / lifetime
The conventional way to implement exponential growth is:
stock = INTEG( - outflow, initial stock ) ~ stuff
outflow = stock * loss rate ~ stuff/time
or
outflow = stock / lifetime
- Fri Jul 28, 2023 2:38 am
- Forum: Vensim
- Topic: Units Check whack-a-mole
- Replies: 9
- Views: 1142
Re: Units Check whack-a-mole
The Log(Pop) error can be handled by defining something like unit pop == 1 ~ person and then normalizing logpop = log( pop/unit pop + 1 ) The other two errors seem like a unit problem with knowledge. Flows always have units of their associated stock, divided by the time unit. Therefore if learning a...
- Thu Jul 27, 2023 5:01 am
- Forum: Vensim
- Topic: Exogenous data in transportation model
- Replies: 8
- Views: 1359
Re: Exogenous data in transportation model
PLE doesn't include the stats tool unfortunately. You could generate a table and copy/paste to Excel or something for the comparison.
- Thu Jul 27, 2023 4:58 am
- Forum: Vensim
- Topic: The use of 'TIME STEP' in equations
- Replies: 8
- Views: 704
Re: The use of 'TIME STEP' in equations
However ... the TREND function does essentially what I proposed, without requiring the extra equation.
- Tue Jul 25, 2023 9:43 pm
- Forum: Vensim
- Topic: The use of 'TIME STEP' in equations
- Replies: 8
- Views: 704
Re: The use of 'TIME STEP' in equations
It sounds like you're trying to recover the value of a variable at a previous time step? This appears to be computing a growth rate or derivative? You could write something like: Previous Resident Income = SMOOTH(Resident Income,TIME STEP) income trend = ( (Resident Income - Previous Resident Income...
- Mon Jul 24, 2023 1:22 am
- Forum: Vensim
- Topic: Response Time
- Replies: 0
- Views: 6636
Response Time
Many of us are at #ISDC2023 so response times will be longer this week.
- Mon Jul 24, 2023 1:10 am
- Forum: Vensim
- Topic: a simple example of my gnarly IF THEN ELSE problem (bug?)
- Replies: 8
- Views: 655
Re: a simple example of my gnarly IF THEN ELSE problem (bug?)
Correct - no - because then there would be no value to assign to the LHS.
- Mon Jul 24, 2023 1:08 am
- Forum: Vensim
- Topic: a gnarly IF THEN ELSE problem
- Replies: 9
- Views: 1002
Re: a gnarly IF THEN ELSE problem
Your translation has two clauses for # if false that Time-sy <= 0 - you can get rid of the second q = 1 ), Then it can be implemented as q = IF THEN ELSE( pE < w , {# if true that pE < w} IF THEN ELSE( Time-sy <= 0 , {# if true that Time-sy <= 0} {q =} 1 , {# if false that Time-sy <= 0} IF THEN ELSE...
- Mon Jul 24, 2023 12:32 am
- Forum: Vensim
- Topic: a simple example of my gnarly IF THEN ELSE problem (bug?)
- Replies: 8
- Views: 655
Re: a simple example of my gnarly IF THEN ELSE problem (bug?)
The only assignment in Vensim is to the left hand side variable. If you want to make multiple assignments, you can use distinct variables, or subscript elements. You can't make multiple assignments within a single equation.
- Mon Jul 24, 2023 12:28 am
- Forum: Vensim
- Topic: a gnarly IF THEN ELSE problem
- Replies: 9
- Views: 1002
Re: a gnarly IF THEN ELSE problem
The Vensim language doesn't support that kind of procedural code. I'm not sure it improves readability over nesting.
- Sun Jul 23, 2023 7:33 pm
- Forum: Vensim
- Topic: Start new models failed
- Replies: 15
- Views: 1048
Re: Start new models failed
I hope this means it's working?
- Sun Jul 23, 2023 7:31 pm
- Forum: Vensim
- Topic: a gnarly IF THEN ELSE problem
- Replies: 9
- Views: 1002
Re: a gnarly IF THEN ELSE problem
I think your simplification is incorrect, because it doesn't nest. It should look li
IF THEN ELSE( a=b, c
, IF THEN ELSE( d=e, f, g)
)
IF THEN ELSE( a=b, c
, IF THEN ELSE( d=e, f, g)
)
- Sun Jul 23, 2023 7:27 pm
- Forum: Vensim
- Topic: a simple example of my gnarly IF THEN ELSE problem (bug?)
- Replies: 8
- Views: 655
Re: a simple example of my gnarly IF THEN ELSE problem (bug?)
This kind of looks like procedural code in the equation field. You can't do that, by design.
100
c*d
is read as
100 c*d
(after condensing the whitespace).
This would have to be
100 <operator> c*d
where <operator> is + - * / ^ in order to make sense.
100
c*d
is read as
100 c*d
(after condensing the whitespace).
This would have to be
100 <operator> c*d
where <operator> is + - * / ^ in order to make sense.
- Sun Jul 23, 2023 7:17 pm
- Forum: Vensim
- Topic: Start new models failed
- Replies: 15
- Views: 1048
Re: Start new models failed
We split it into two ... won't update the video until later, because there's a big update for these tools in the pipeline.
- Fri Jul 21, 2023 2:22 pm
- Forum: Vensim
- Topic: Start new models failed
- Replies: 15
- Views: 1048
Re: Start new models failed
Not having seen this before, I'm pretty stumped. When the pred-prey model opened, could you interact with it? "PL9999" is the standard s/n for all academic PLE, so unfortunately that doesn't provide a clue. Long shot, but anything unusual about the environment? (multiple monitors, remote a...
- Fri Jul 21, 2023 1:33 pm
- Forum: Vensim
- Topic: Exporting large sensitivity output
- Replies: 2
- Views: 453
Re: Exporting large sensitivity output
You could use a savelist or SAVEPER to reduce the scale of the data.
You could also try the relational Data List format or .dat (though the latter is not really friendly to other apps). Both will be large.
.tab is probobly no better, and .xls is surely worse.
You could also try the relational Data List format or .dat (though the latter is not really friendly to other apps). Both will be large.
.tab is probobly no better, and .xls is surely worse.
- Thu Jul 20, 2023 5:27 pm
- Forum: Ventity
- Topic: GIS in Ventity
- Replies: 1
- Views: 1535
Re: GIS in Ventity
There isn't ... but I'll create something after the SD conference.
- Thu Jul 20, 2023 5:02 pm
- Forum: Vensim
- Topic: v.10 Parallel computations
- Replies: 2
- Views: 996
Re: v.10 Parallel computations
You can use the DSS trial key on the conference page if you'd like to experiment.
https://vensim.com/conference/
https://vensim.com/conference/
- Thu Jul 20, 2023 4:28 pm
- Forum: Vensim
- Topic: Delay Function cannot shut off flow using a test for negative stock level.
- Replies: 18
- Views: 4063
Re: Delay Function cannot shut off flow using a test for negative stock level.
Well I must be dumb too, because I hadn't figured it out yet either!
I generally prefer the array version over the conveyor function. It's more flexible, because you can have multiple outflows (separate decay and uptake, for example), or nonlinear uptake.
I generally prefer the array version over the conveyor function. It's more flexible, because you can have multiple outflows (separate decay and uptake, for example), or nonlinear uptake.
- Thu Jul 20, 2023 3:06 pm
- Forum: Vensim
- Topic: Start new models failed
- Replies: 15
- Views: 1048
Re: Start new models failed
I can't immediately think of a reason. My OS versions (13.1 and 10.something) bracket yours, and PLE works fine on both. The only thing I can think of is an expired evaluation license, but normally the application declines to start rather than freezing. Solution would be to reinstall using the educa...
- Tue Jul 18, 2023 4:28 pm
- Forum: Vensim
- Topic: Delay Function cannot shut off flow using a test for negative stock level.
- Replies: 18
- Views: 4063
Re: Delay Function cannot shut off flow using a test for negative stock level.
In this case, I think you can forget about my rigid and elastic pipe variants, and just use the classic aging chain. There are two options for this: - If the loss function is a simple fractional rate (uptake, or radioactive decay), you can use the DELAY CONVEYOR with leakage. There's an example inst...
Re: DBLPREC
I think this thread viewtopic.php?t=8116 established that the error is caused by a missing : at the beginning of a macro.
Re: DBLPREC
Rather than defining these in the code, you probably want to define them in the preprocessor, via /D "DBLPREC". In Visual Studio this is in project properties>C/C++>Preprocessor.