Re: Considering a new project & wanting something for nothing

[Jan Kreft]

Paul,

I'm wondering how important is space in your sim? I got the impression
that agents will move around a lot, so position is only temporary and not
a useful info to store. You could just abandon space altogether and have
everyone sitting in front of a phone and just let them call others at
random and memorize phone calls like calling #207 was a rather pleasant
experience, etc. And this comes from someone who believes strongly in the
importance of spatial heterogeneity ;-) Once agents have some memory about
prev. calls, they will start to call less numbers at random. The memory
about what one learned from whom should be within the agent and not in the
space, which is a passive meeting ground at best, anyway.

Best regards, Jan.

Jan Kreft                               Phone +44 (0)1222 876036
Cardiff School of Biosciences           Fax   +44 (0)1222 874305
Cardiff University                      E-mail address@hidden
PO Box 915, Cardiff CF1 3TL, UK

On Wed, 9 Jun 1999, Paul Johnson wrote:

> 
> Last fall, I signed up to give a paper at a meeting that will be held
> this fall.  The paper is about different models of opinion formation and
> social influence and one variant that I'm considering now goes roughly
> like this.  We want 
>    1. Individuals who look about for "discussion partners".  They search
> within a "neighborhood" for people they expect will give pleasant
> conversation.  They choose at random among all targets that are equally
> likely to be pleasant.  Pleasant is some combination of agreement with
> own opinion and usefulness in other respects (they may have a hamburger
> you want, etc.)
>    2. There can be discussion between the partners and certain amounts
> of information revealed.  A friend who is a professor at Indiana has
> done lots of empirical work and claims that the other person's opinion
> will have more impact if that person is seen as knowledgable, for
> example.  There are plenty of little details that may have to be ignored
> in the model.
>    3. On the basis of their discussion, individuals can change their
> opinions.  Their knowledge level may be incremented as well, if they
> were a less knowledgable person talking to a more knowledgable person.
>    4. Then they proceed to look for more discussion partners.  There has
> to be some ingredient that creates a tendency to go back to the same
> discussion partners, but also a willingness to look for new ones.
> 
> I have been thinking about this for a little while, but didn't work yet
> on designing a simulation.  If you have ideas about it, I'd be glad to
> hear.
> 
> Anyway, I got to looking at an app that Pietro Terna is distributing
> called LangtonAntSpace.  I've got version 0.8, but there may be newer
> ones. Anyway, he has an updated version of Sven's upgraded MoGrid2d
> class in there.  That is a  class in which there is a 2d grid, and at
> each one there can be a list of occupants.  The class looks to be well
> designed (thanks, Sven) and updated (thanks Pietro).  Takes into account
> Swarmlib changes through 1.4.
> 
> So I got to thinking like this.  What if the world of each agent is
> thought of as a MoGrid2d, and an agent can enter a space on the lattice,
> and then discuss with some elements from the list, then form an opinion
> about the people in that space, and possibly decide to stay or go.  If
> the agent stays, then its participation will affect other agents looking
> to move as well.
> 
> Then I started to wonder how I would design record-keeping for each
> agent, a tally of experiences in each cell.  I think I would create a
> Tally object for each cell visited, and in there store whatever
> information was obtained.
> 
> I started thinking about creating a Grid2D object inside each agent and
> hanging the Tally objects on the right spots. (Even though the Grid2D
> documentation says it is a space for agents, I don't think it would mind
> holding some other kinds of objects :).    
> 
> But then I wondered if there is a way to get something for nothing. 
> Since the MoGrid2d class can answer a message like "getListatX:Y:", and
> it returns a Swarm list object, it seems like I'm getting something for
> nothing by using a Swarm Map with the return from "getListatX:Y:" as the
> key and the Tally object as the item.  I don't have to allocate any
> dynamic memory that way, but I do pay a performance penalty of slow
> searches through the Map for a particular list.
> 
> I see a major danger in either of these approaches, however. If a spot
> in the MoGrid2d goes "empty" after an agent has been there, then the
> agent will still possess a Tally for that spot, even though the spot
> does not exist.  If an interation over a Map tries to use a key that no
> longer exists, I think that agent would meet Mr. Segmentation Fault.  
> 
> But I don't want to have the MoGrid2d class having to notify every agent
> when a list goes empty in the grid, right? 
>    
> 
> -- 
> Paul E. Johnson                       email: address@hidden
> Dept. of Political Science            http://lark.cc.ukans.edu/~pauljohn
> University of Kansas                  Office: (785) 864-9086
> Lawrence, Kansas 66045                FAX: (785) 864-5700
> 
> 
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