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vensim PLE question
Posted: Mon Sep 13, 2010 2:42 am
by zhouchchun
how to calculate p(i)-p(i-1) in vensim PLE, please help me, thank you !
Posted: Mon Sep 13, 2010 7:10 am
by Administrator
I don't know if PLE has DELAY FIXED, but you can use that to store the value of P at time-1.
P at last time step = DELAY FIXED ( P, time step, 0 )
value = p - P at last time step
Tony.
Thanks
Posted: Mon Sep 13, 2010 9:32 am
by zhouchchun
Thank you, Tony, you help me very much
Posted: Mon Sep 20, 2010 10:48 pm
by tomfid
As long as you're using Euler or Diff integration, you can also use SMOOTH(p,TIME STEP).
It's worth pondering why you want a discrete delayed value - generally people are using this to either calculate derivatives or run discrete time models, both of which have pitfalls.
Tom