Hi,
I was using the delay macro in vensim and realized how one needs to be careful with TIMESTEP when using the macro.
Instance - suppose its a 6th order delay and I have a total delay time of 1, then the delay in each of the stocks is 1/6. Which meant to me that my earlier DT of 0.25 was not right ( I had gone by the thumb rule of DT being 1/4th of the smallest time constant - without factoring for the break-up of the delay time in six stocks)
Was wondering how does Vensim handle this problem in a delay with infinite order - the delay fixed macro given that one is still integrating the stocks?
Malli
Re: Delay Fixed and Integration Error in Vensim
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bob@vensim.com
- Senior Member
- Posts: 1107
- Joined: Wed Mar 12, 2003 2:46 pm
Vensim has only 3rd order delay macros (DELAY3, SMOOTH3) and the time constant in those is 1/3 of that input. So if you are using any of these be careful.
DELAY FIXED is not implemented as a macro but a function - it stores the time at which a value should be emitted and is not dependent on time step except that during every computation it needs to store new values.
The function DELAY N will automatically detect conditions where nonsense would occur and reduce the order of the delay - it does issue a warning when this happens.
DELAY FIXED is not implemented as a macro but a function - it stores the time at which a value should be emitted and is not dependent on time step except that during every computation it needs to store new values.
The function DELAY N will automatically detect conditions where nonsense would occur and reduce the order of the delay - it does issue a warning when this happens.