Ventana software support forum

Hi there,

Please is there any technique or function I can use to hold the value of a variable such that variable "A" at time T or T+1 will have the value of a variable "B" at that "T" or "T-1" respectively. Many thanks

Olu

Take a look at SAMPLE IF TRUE or DELAY FIXED. One of these should do what you need.

Tony.

perhaps mixed it up..I need a function that can perform the opposite of the delay function i.e a function that will let a variable "A" at time T to hve a value of a variable "B" t time T+1

Vensim (and reality) is causal - that is, no variable can use information about the future.

Can you say more about the reason for this approach?

cheers Tom, in the attache model for example, I need a function that will let variable "y" have values of 0.94, 0.909651...at times t= 1 and 2 ....theoretically i know it isnt right but I need it or some analysis...tnx

There is no function that can do that. You can try using FORECAST or TREND. Otherwise, you would need to calculate the model a time step in the future.

There is a trick you could do though - cumbersome in general, but feasible in a simple model. Create an auxiliary that calculates the value of the stocks ahead a unit of time (assuming Euler integration):

future bad code = bad code + roc*TIME STEP

Then use can use the "future" stocks to calculate other future variables.

cheers Tom!!!should have thought of that

The other possibility is to just put minus signs in all your integrations, and run the whole model backwards.

splendid!!