Ramp function

[nadia]

Hi everybody,

How to use the ramp function?in my sd model, actual data shows that per capita consumption of rice shows a declining trend at 1percent over the year. Therefore, how im going to put in this scenario in my model? is it possible for me to use the ramp function?By the way Im using vensim.Thank you in advance.


Regards,
Nadia

[Administrator]

The help system explains how to use it.

http://www.vensim.com/documentation/ind ... ?22670.htm

Use something like
percentage decrease = RAMP ( -0.1 , INITIAL TIME, FINAL TIME )

[tomfid]

A linear ramp, as in the RAMP function, is not necessarily what you want. If the 1%/yr change is compounding, you can use a stock to represent that:

rice demand = INTEG( rice dem changing , init rice demand) ~ kg/person/yr
rice dem changing = rice demand*rice dem change rate ~ (kg/person/yr)/yr
rice dem change rate = -0.01 ~ fraction/yr

If the rate of change is constant, you can use the exponential solution to this directly,

rice demand = init rice demand*EXP( rice dem change rate*(Time-INITIAL TIME))

Tom