easier way to monitor a sequence from ezgraph?

[Paul E Johnson]

Dear Swarmish folk.

Today I decided I wanted a simulation to stop when an indicator in an 
EZGraph reached a certain value.  And when the model stops, I want a 
pixmap of the EZGraph.  (Hence I asked earlier about things at quit time).


SO I figured how to use probes! (Big Personal Breakthrough there, eh.) 
Anyway, I create a sequence and probe into it to get the averager object 
out of it, and then schedule so that when the value reaches 0, the sim 
stops.  Here's how I did it:

id nchanges; //an averager object grabbed out of sequence

 {
    [opinionGraph createSequence: "Opinion = YES"
                      withFeedFrom:  [modelSwarm getInfluenceGrid]
                       andSelector: M(getPctTypeOne)];
                
    {
      id aseq = [opinionGraph createAverageSequence: "Opinion Changed"
                  withFeedFrom: [modelSwarm getCitizenList]
                  andSelector: M(getChanged)];
      id probe = [VarProbe createBegin: self];
      [probe setProbedClass: [aseq getClass]];
      [probe setProbedVariable: "averager"];
      probe = [probe createEnd];
      nchanges = (Averager *) [probe probeAsPointer: aseq];
    }
}

I've checked and getAverage calls to nchanges do get answers.

This seemed like a long way around the castle to find out the current 
value of a sequence object.  Is there an easier way to do it in the 
current Swarm?  If not, what would be the objections against me digging 
into the Swarm source and adding an IVAR to any sequence called 
"currentValue" or something and a method "getCurrent" to retrieve it?


Oh, one more thing.  This is a numerical thing. I remember Ted Belding's 
caution about checking floating point numbers for equality. If you 
wanted a simulation to end when the average is 0, how likely with there 
be trouble if I compare a double against 0:

if ([nchanges getAverage] == 0)

Is it a one-in-ten problem or a one-in-one-million problem ?

--
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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