Active vs. Initial Problem/Bug?

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hazhir
Junior Member
Posts: 11
Joined: Tue Sep 10, 2024 2:51 pm
Vensim version: DSS

Active vs. Initial Problem/Bug?

Post by hazhir »

Hi,
In simulating the attached model I get weird behaviors, where some 'Initial' variables are simulated incorrectly (and I get warnings for Active/Initial difference). Specifically, check out:
1- 'Sum Initial Buildings' vs. 'Desired Current Buildings' at time zero. The two should be the same but they are not.
2- 'Utility of Alternative Locations' vs. 'Average Realized Utility'. Again, the two should be the same but they are not.
I don't know what is happening, it has been a pain, and it is the first time I am seeing this type of inconsistency. Any insights on what may be going on and how to fix it?

Thanks a lot!
Hazhir
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SimpleCity-V05_4.mdl
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Administrator
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Joined: Wed Mar 05, 2003 3:10 am

Re: Active vs. Initial Problem/Bug?

Post by Administrator »

I'm not back in the office until the new year. Here is some additional debug information in case it helps.

DEBUG:ERROR: Math error (underflow) computing : #Perceived Weighted Product Price>DELAY1I>LV1#[BService].
DEBUG:ERROR: Check causes and uses of #Perceived Weighted Product Price>DELAY1I>LV1#[BService] for division by zero or overflow.

There is an "underflow" error (https://stackoverflow.com/questions/422 ... flow-occur) when calculating "Perceived Weighted Product Price". I'd suggest replicating the DELAY1I macro manually to see if one of the calculations is too small. Once the active/initial problems have been eradicated, I'm sure all will be ok.
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aliakhavan89
Senior Member
Posts: 162
Joined: Sun Oct 21, 2018 7:09 am
Vensim version: DSS

Re: Active vs. Initial Problem/Bug?

Post by aliakhavan89 »

I think the initial value for 'Impact of Affordability on Housing Demand' is causing an issue. I used the values at time=0 as initial, and 'Sum Initial Buildings' and 'Desired Current Buildings' match at the beginning of the simulation, though there's a change in model behavior.
Screenshot 2024-12-27 at 11.53.42 AM.png
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SimpleCity-V05_4_AA.mdl
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hazhir
Junior Member
Posts: 11
Joined: Tue Sep 10, 2024 2:51 pm
Vensim version: DSS

Re: Active vs. Initial Problem/Bug?

Post by hazhir »

Thanks so much Alireza; that initial value was not needed and removing it indeed solved the problem!
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