Combat Modelling

[Lanchester]

Hi folks,

my problem is the following: I'd like to represent the Lanchester Laws in Vensim.

Lanchester's laws are mathematical formulae for calculating the relative strengths of a predator–prey pair, originally devised to analyse relative strengths of military forces.

The Lanchester equations are differential equations describing the time dependence of two armies' strengths A and B as a function of time, with the function depending only on A and B.


I've tried to implement this in Vensim but met problems really early.

The basic model is, that there are two opposing forces with an initial number of soldiers attacking each other with a different effectiveness, depending on the number of soldiers. So when the fight goes on, day by day, the number of soldiers should shrink, until one army is wiped out and the other force is the winner.

When trying to build this in Vensim, I've encountered several "simultaneous equations errors".

My questions are:

1. How can I portray this model effectively using Vensim?

2. How can I deal with the simultaneous equations errors (I didn't really find something in this forum fitting to my problem) or maybe how can I write the code that they attack consecutively?

3. How can I tell the model to stop when one of the forces is annihilated(The number of soldiers from one forces reached zero)?

Here is what I've been up to lately:

aimed fire model2.mdl

(3.58 KiB) Downloaded 191 times

This is my first time modelling with Vensim and I would be glad if someone is able to help me.

Have a nice day

[Administrator]

You are going about this in the wrong way.

Start here and go through the PLE tutorial.
http://www.public.asu.edu/~kirkwood/sysdyn/VenPLE.pdf

This will introduce you to stocks and flows.

Now think of the blue/red forces as stocks, and the rate they are destroyed as flows. I've attached a model which does things in more or less the right way for you.

aimed fire model forum.mdl

(3.4 KiB) Downloaded 195 times

I haven't entered units for some of the parameters (as I don't know what they should be).

From memory, the Lanchester equations also include some terms for the relative sizes of the red/blue forces, you'll need to add those as well.

[Lanchester]

Wow, I am quite impressed and a bit frustrated that you did a far better job than me in such a short time.

Nevertheless, many thanks for your advice and your help!

Have a good weekend or at least a nice Sunday.