I am using the trial PLE version to assess whether it suits my needs (and whether I can drive it).
Starting with a simple flow of petroleum cargo imports, storage, despatch and replenishment, with some stochastic variables. I have yet to find how to introduce a random delay to model variable vessel discharge times (eg vessel can be 1 day early or up to 2 days late due to berth congestion etc).
I can see fixed period delays (which I will use for order to on water time) but nothing that gives, say, a normally distributed random delay.
In another tool I vaguely remember using a random number generation step and then, separately, an equation that draws on that random number to effect a delay.
Any suggestions about how to model the delay stochastically?
How to model random delay within min/max?
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Re: How to model random delay within min/max?
That is exactly what you do in Vensim as well.In another tool I vaguely remember using a random number generation step and then, separately, an equation that draws on that random number to effect a delay.
First generate the random number
http://www.vensim.com/documentation/ind ... random.htm
Then use delay material
http://www.vensim.com/documentation/ind ... terial.htm
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Re: How to model random delay within min/max?
Thanks for the tips.
WIth Delay Material unavailable in PLE (or PLE Plus) I am looking for a workaround.
WIth Delay Material unavailable in PLE (or PLE Plus) I am looking for a workaround.
Re: How to model random delay within min/max?
To have a variable delay you need the delay material function not available in the PLE version.
The solution is to use several delay fixed variables with a different delay each, and then to choose which delay to use depending on
a random function.
Regards.
JJ
The solution is to use several delay fixed variables with a different delay each, and then to choose which delay to use depending on
a random function.
Regards.
JJ
Re: How to model random delay within min/max?
Thanks JJ ... Focusing on bigger alligators in my model, but will come back to explore your suggestion.
Michael
Michael
Re: How to model random delay within min/max?
A normally distributed delay is not physically possible, because it includes negative arrival times. Practically, this may not be an issue, if the mean is large such that the probability of a negative arrival time is vanishingly small. But generally, you want something like a Poisson process (RANDOM POISSON) that has some grounding in theory.
There's an example here:
http://models.metasd.com/rental-car-sto ... -dynamics/
There's an example here:
http://models.metasd.com/rental-car-sto ... -dynamics/
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Re: How to model random delay within min/max?
An updated link:
http://metasd.com/2010/04/rental-car-st ... -dynamics/
http://metasd.com/2010/04/rental-car-st ... -dynamics/
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