Re: fest discussion

[Robert E. Bell]

Hey Doug...

I think the model verification discussion is a very good idea. You
can definitely count me in (possibly Melissa)...I'm planning on doing
my model verifications of arborscapes  (arborgames grew up and started
using real data ;-)   this summer.   Are you going to organize it?

Robert


Doug Donalson; wrote:

> Is anyone interested in putting together and discussion
> group on model testing and verification at SWARM fest?
>
> Here is my "take" on it with examples from my research.
>
> One of the most difficult and important aspects of complex
> modeling is that of model testing and verification.  It
> falls into two broad catagories, verifying that the model
> is bug free, and determining the effects of what I call
> model infrastructure.
>
> Two examples of the first catagory:
>
> Test individual components:
>
>    Ex: I have an agent that in the absence of all other
>        effects dies off exponentally so I turn off all
>        other effects and confirm that all the individuals
>        die off and that the half life time matches the
>        death rate.
>
> Compare with simpler models:
>
>    Ex: I have a "base line" delay differential equation
>        model that provides stability boundries and
>        equlibrium values for a set of parameters.  I
>        developed a second model that is the analog of
>        the DDE but with the quantization effects associated
>        with requiring the number of individuals to be
>        an integer.  This is the Stochastic Birth/Death
>        or SBD formulation.
>
>        If I force my complex model to be "well mixed"
>        spatially, then it should match the results of the SBD
>        for the same system size and parameter choices.  The
>        SBD model can then provide the parameter space
>        where the quantization stochasticity has a small
>        effect on the system dynamics.  This allows a
>        set of parameters or "parameter space" in which
>        my complex model should have very similar results
>        to the DDE model.
>
>        Bottom line: I find a parameter space that if my complex
>        model is working correctly it should provide results
>        that match those of an analyticaly (or at least
>        numerically) tractable model.
>
> The second catagory has to do with the effects that the
> actual model implimentation may have on the results.
> This is basically worrying about artifacts from model
> structure.
>
>       Ex: Any time you design a model around a lattice
>           structure you by definition quantize space.
>           Does this "minium size" of one square have
>           a significant effect on the results?
>
>       Ex: When using a synchronous schedule how does the
>           ordering of events within a time step affect
>           the outcome.  For example, if it was a predator/prey
>           simulation, if predation always came before prey
>           birth you would potentially expect a different
>           outcome then if births came before predation.
>
> I know this is long winded, but these are key issues if
> we are to believe and understand the results of complex
> models.  Is anyone interested in tossing around problems
> and solutions in these areas?  Let me know if anyone is
> interested.
>
> Cheers,
>
>    Doug Donalson
>
> ***************************************************************************
> * Doug Donalson                          * Office: (805) 893-2962         *
> * Ecology, Evolution, and Marine Biology * Home:   (805) 961-4447         *
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> *                                                                         *
> *   The most exciting phrase to hear in science, the one that             *
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--
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of life: that word is love.  --- Sophocles

Earth provides enough to satisfy every man's
need, but not every man's greed.  --- M. Gandhi

*****************************
Robert E. Bell
Department of Geography
University Of California, Los Angeles
Email: address@hidden



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   with "help" in the body of the message.
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