't' is not a variable name
Posted: Tue Sep 27, 2022 8:25 pm
Good day, I'm working on the car population model in Donnella Meadow's book Thinking in Systems, and the formula for the population
Level object is given as:
Stock: population(t) = population(t - dt) + (births - deaths) × dt Initial stock value: population = 6.6 billion people
I tried to whittle it down to: population(t - dt) + (births - deaths) x dt
It has been awhile since I've used vensim(, since Vensim PLE - I'm running Vensim PLE Plus 8.2.2 x64)
I thought the problem was that her model was written in Stella, but I got the same error.
e: Unit errors Yes - this looks right. You'll see this notation in the literature a lot:
The note at the top of the forum: "dStock/dt = rateConstant * Stock
or in discrete time: Stock(t) = Stock(t-dt) + dt*(rateConstant*Stock)
which is equivalent to Vensim: Flow = rateConstant*Stock Stock = INTEG( flow, initval ..."
I tried to work that out and get rid of the error " 'but I'm having a rough time.
Can anyone do a translation for me, the new syntax is confusing.
Thank you.
Level object is given as:
Stock: population(t) = population(t - dt) + (births - deaths) × dt Initial stock value: population = 6.6 billion people
I tried to whittle it down to: population(t - dt) + (births - deaths) x dt
It has been awhile since I've used vensim(, since Vensim PLE - I'm running Vensim PLE Plus 8.2.2 x64)
I thought the problem was that her model was written in Stella, but I got the same error.
e: Unit errors Yes - this looks right. You'll see this notation in the literature a lot:
The note at the top of the forum: "dStock/dt = rateConstant * Stock
or in discrete time: Stock(t) = Stock(t-dt) + dt*(rateConstant*Stock)
which is equivalent to Vensim: Flow = rateConstant*Stock Stock = INTEG( flow, initval ..."
I tried to work that out and get rid of the error " 'but I'm having a rough time.
Can anyone do a translation for me, the new syntax is confusing.
Thank you.