Ventana software support forum

Hi
I am, PhD scholar of entomology. My thesis is about prey and predator. I would like to develop a vensim model.
I’ve calculated the longevity of adults. I’d like to know how I can use it in. I want to remove produced adults from model cycle gradually,

If longevity is known, why don't you formulate deaths as adults/longevity?

The previous post is correct,
To make sure you keep the "adults" stock positive, use the following equation (it takes everything from the stock, or what it needs).

You should also add units to your model.

HI
Here is joined a possible model. I have added units and use strictest unit testing (in the unit setting window). You should study and understand them. I have too added minimum, maximum and increment to the constants to be able to make them vary with the synthesim and added two graphs for the levels. You should use intensively the synthesim to build multiple scenarios and understand for each of them the behavior of each of the variables. One good idea is to override the behavior of any variable while in synthesim mode by right clicking on the variable if you have this feature implemented in your Vensim version. Using this model fully will take quite a time and will help you in building a more complete model.
Regards.
JJ

Administrator wrote:The previous post is correct,

Code: Select all

deaths = adults / longivity

To make sure you keep the "adults" stock positive, use the following equation (it takes everything from the stock, or what it needs).

Code: Select all

deaths = min ( adults / time step , adults / longivity )

You should also add units to your model.

Since "adults" has first-order negative feedback control, I do not believe the MIN function to be required.

Since "adults" has first-order negative feedback control, I do not believe the MIN function to be required.

Correct - assuming that longevity >= TIME STEP, which should definitely be the case.

Some possible examples:
http://models.metasd.com/lotka-volterra/ the classic LV model
http://models.metasd.com/early-warnings-of-catastrophe/ a version with separate adult and juvenile cohorts
http://models.metasd.com/bifurcating-salmon/ a fisheries model with separate age cohorts and discrete time
The source literature for these might also provide some good references.