Ventana software support forum

i want to calculate the demand's STD,

can some one tell me how to do it?

does it have any function in vensim can use to calculate one variable's STD

thank you ....

the stats tool will report the standard deviation of a variable over a simulation.

i don't understand your meaning.

can you explain clear to me

thakn you ...

Chapter 14 of the Refrence Manual describes the Stats tool.

thank you !

but if want to collect at t=1 STD, then use this number to calculate something

how to do it

You can only see current values in model equations. To get a standard deviation over time requires multiple time values. You may be able to invent some equations that compute this for past time - if you do post them here as other people may also be interested.

Hi

Joined a model where you have every time steps, a set of variables generated randomly but can be loaded from real data, and that calculates each time step, the mean and the standard deviation of the set of variables. Vensim pro needed.
Regards.
Jean-Jacques Laublé

hi,

if the experience is not a set, just a constant or a uumber, can i use this model?

because i want to calculate the demand's STD, and every week's demand is different, i want to get the STD, then to calculate the ROP.

hope you know my means,

thank you .

Hi

You need to be more explicit about your needs.

The standard deviation is not necessarily the solution to your problem.

If you want the std from a variable, you have to define a trend for that variable, wich is for every time step, an expected value for that variable base on its historical data, and then calculate the standard deviation of the real value from that expected value.
The simpler solution and generally the more efficient to predict the demand is to take a running average eventually
weighted with the oldness of the data.
Did you study the afore mentioned chapters from business dynamic's?
Regards.
JJ