Hello everyone,
I have a problem to run my model. Initially it was OK, but once i put a shadow variable as an input to this one variable, and poof! the error came out.
I had read the solution in previous same topic as mine here, but i don't think my problem is the same.
Attached is the screenshot of my model, as well as the .mdl file of it.
Your help is much appreciated.
Simultaneous Equation Error
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Simultaneous Equation Error
- Attachments
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- Without the variable
- Without New Installed Cap variable.png (138.6 KiB) Viewed 3866 times
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- Without the variable
- With New Installed Cap variable.png (139.39 KiB) Viewed 3866 times
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- where i define the variable
- New Installed Cap.png (230.37 KiB) Viewed 3866 times
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Re: Simultaneous Equation Error
The .mdl file.
I left it in my previous post.
I left it in my previous post.
husnafezaahmad wrote: ↑Fri Feb 07, 2020 8:16 am Hello everyone,
I have a problem to run my model. Initially it was OK, but once i put a shadow variable as an input to this one variable, and poof! the error came out.
I had read the solution in previous same topic as mine here, but i don't think my problem is the same.
Attached is the screenshot of my model, as well as the .mdl file of it.
Your help is much appreciated.
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Re: Simultaneous Equation Error
Which two variables are you referring to?husnafezaahmad wrote: ↑Fri Feb 07, 2020 8:16 ambut once i put a shadow variable as an input to this one variable, and poof! the error came out.
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Re: Simultaneous Equation Error
I'm guessing that you are using the wrong equation for "new coal". You are using the STEP function, I suspect that you want a delay here instead.
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Units are important!
http://www.bbc.co.uk/news/magazine-27509559
http://www.ventanasystems.co.uk/forum/v ... f=2&t=4391
Units are important!
http://www.bbc.co.uk/news/magazine-27509559
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Re: Simultaneous Equation Error
OMG! Yes, i want a delay over there. Thought that STEP can also be treated as delay thanks! I’ll work on it and i really pray it’ll work.
Administrator wrote: ↑Fri Feb 07, 2020 8:59 am I'm guessing that you are using the wrong equation for "new coal". You are using the STEP function, I suspect that you want a delay here instead.
Re: Simultaneous Equation Error
I think the .mdl attachment was omitted.
Looking at the diagram, it seems like there's an issue with the regression. I'm not sure whether the "load growth" stock has units of energy (additional load above some baseline) or energy/time (rate of change of load). But both seem problematic:
additional load {kw} = f( population {people}, GDP {$/yr} )
might be ok, but could be non-robust if (for example) low values of the inputs cause negative load.
load growth rate {kw/year} = f( population {people}, GDP {$/yr} )
is really problematic because it's mixing stocks and flows, i.e. regressing through an integration.
Looking at the diagram, it seems like there's an issue with the regression. I'm not sure whether the "load growth" stock has units of energy (additional load above some baseline) or energy/time (rate of change of load). But both seem problematic:
additional load {kw} = f( population {people}, GDP {$/yr} )
might be ok, but could be non-robust if (for example) low values of the inputs cause negative load.
load growth rate {kw/year} = f( population {people}, GDP {$/yr} )
is really problematic because it's mixing stocks and flows, i.e. regressing through an integration.
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Re: Simultaneous Equation Error
Here is my file. Dunno why it was omitted.
Since i'm so new in this vensim world, i'm kinda confused tho with the suitability for one variable to either be stock or not.
Since i'm so new in this vensim world, i'm kinda confused tho with the suitability for one variable to either be stock or not.
tomfid wrote: ↑Fri Feb 07, 2020 10:50 pm I think the .mdl attachment was omitted.
Looking at the diagram, it seems like there's an issue with the regression. I'm not sure whether the "load growth" stock has units of energy (additional load above some baseline) or energy/time (rate of change of load). But both seem problematic:
additional load {kw} = f( population {people}, GDP {$/yr} )
might be ok, but could be non-robust if (for example) low values of the inputs cause negative load.
load growth rate {kw/year} = f( population {people}, GDP {$/yr} )
is really problematic because it's mixing stocks and flows, i.e. regressing through an integration.
- Attachments
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- 1st Objective V3.mdl
- (57.73 KiB) Downloaded 158 times
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Re: Simultaneous Equation Error
I’m still struggling with this simultaneous error.
Can anyone help me?
Can anyone help me?
Re: Simultaneous Equation Error
The version attached above runs for me - not clear how to replicate the error.
The issue is likely a feedback loop without a stock in it. I think this model would benefit from a complete rework of the stock-flow usage. Start by going through and getting rid of the boxes on anything that is not a stock (level) and doesn't use a function with an internal level (SMOOTH or DELAY functions).
The regression definitely seems problematic. Consider what happens if population and GDP are constant: load grows at a constant rate. Why would that happen?
The issue is likely a feedback loop without a stock in it. I think this model would benefit from a complete rework of the stock-flow usage. Start by going through and getting rid of the boxes on anything that is not a stock (level) and doesn't use a function with an internal level (SMOOTH or DELAY functions).
The regression definitely seems problematic. Consider what happens if population and GDP are constant: load grows at a constant rate. Why would that happen?
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