Paul Johnson
Feb. 17, 2000

POLS 909 Swarm Beginner Exercises.

I was struggling to think of things a person can do to gain a
basic level of comfort with Swarm and Objective-C.  I don't want to
rely on any advanced Swarm programming tricks, I want the basics of
objects, methods, and so forth.  So here is what I have come up with.
After you finish reading/working through the Swarm tutorial, you
should be able to manage these things, if you make some effort.

Begin with any "relatively advanced" swarm application, such as
simpleObserverBug2 or heatbugs.  Then try these things.

1. Create a new method in the agent class (Bug or such).  I always
   create a "sayHi" method in my agents, and it has printf statements
   in there that report the agent's variables.  After you have created
   a method that does that (whatever you call it), then in your "step"
   method, or any other method that gets executed, add a message that
   calls your new method.  When your program runs, you should see
   output in your console.

   Question: if you put the new method in Bug.m, but not in Bug.h,
   does it run? (You may get a compiler warning about the method not
   being declared, but the model should run, even though the method is
   not in the interface.)  You may have to remove -Werror from
   Makefile.common in order to make it compile, though.

2. In your ModelSwarm, try to schedule the agent to execute the new
   method you created.  Do that in the buildActions method.  Note
   that, if you want this to work, you have to add your new method to
   the interface file for Bug.h or whatever.  If you don't have that
   method in the interface, part 1 may still work, but for sure this
   step won't work.

3. The method you created in 1 probably did not have any return value
   you wanted to catch.  Now write a new method in your Bug class that
   returns an integer or a floating point value.  I don't care what
   that value is.  Then in your step method name a variable, and set
   it equal to the return value from your new method, as in
      int newVariable;
      newVariable=[self newFunction];

   Then put a printf statement that prints newVariable to the console.

4.  After that works, modify your newFunction so that it takes some
    arguments.  It could take as arguments any variables that are
    available inside the scope of your step method.  Then fiddle the
    newFunction's innards to do something with those values and return
    a result.

Harder/Trickier things to try.

5. Does your ModelSwarm have a "getList" (or similar name) method that
   returns a list of all its objects?  Most of them do have that, and
   it is used primarily by the Observer, which asks the model swarm to
   give it a list for plotting.  If you don't have a getList kind of
   method in ModelSwarm, make one.  Then try this. Figure out a way
   that the Bug class can ask the model swarm for a list, and let the
   Bug keep that list.  Once you think you have the ability to
   retrieve the list in the Bug, and suppose you call that list
   "bugList", then you can do this in your Bug to see if it worked:

	      [bugList forEach: M(sayHi)];
   This, of course, assumes you have a sayHi method in your bug class.

6. If this seems to indicate that you do indeed have the list copied
   into your Bug, then try this in your Bug class.  You can put this
   in the step method or in another method, as long as the method gets
   executed sometime.  Let's grab the first bug in the list,
	    firstbug=[buglist atOffset: 0];
   Then tell that bug to execute some methods, such as sayHi.

7. If you got part 6, next write a method that can grab an agent from
   the list, possibly at random, using the select methods from the
   NSelect class in the simtools library.  You must import simtools.h
   and the NSelect method is declared like this:

+ (void)select: (int)n from: aCollection into:  bCollection;

   Notice that select is a class method, so if you have "buglist" in
      place of aCollection and some "otherList" you created in place
      of bCollection, you can execute it like this: 

      [NSelect select: 1 from: bugList into: otherList];

   There is an easier way to select a single member, you could use the
   uniform integer random variable to pick an integer, k,  between 0 and
   N-1 and then do 
      aBug = [bugList atOffset: k];    
   But I like NSelect for other purposes, so you could try it too.