Spent a few cycles yes­ter­day think­ing about Lau­rent Bossavit’s provo­ca­tion, and while I’m hav­ing fun get­tin’ all com­plex­o­log­i­cal after so many years away from the Santa Fe Style, I’m increas­ingly con­fi­dent it’s not quite what he was ask­ing for.

After all, com­plex sys­tems mod­els offer no pre­dic­tive value, except in the sense that they pro­vide insights into mod­els’ intrin­sic con­se­quences. As with Genetic Pro­gram­ming vs Sta­tis­tics, agent-​​based com­plex sys­tems mod­els are use­ful only inso­far as they sur­prise and inspire fur­ther mod­els, not as tools inter­act­ing with the “real world”.

At any rate, I’m find­ing it a use­ful exercise.

Here’s where I am now, as of this writ­ing (link to old commit).

Per­son­ally I’m con­fi­dent that the toolkit of com­plex­o­log­i­cal mod­el­ing is emi­nently prac­ti­cal; Nk mod­els, Boolean net­works, agent-​​based sim­u­la­tion, all the rest is in my blood, so the design pat­terns are so obvi­ous to me that I can slap some­thing together in a few min­utes. But it’s inter­est­ing as I talk with folks (Lau­rent and Ron Jef­fries, among oth­ers) about this lit­tle sketch, how often my cor­re­spon­dent wants to drop my mod­el­ing toolkit back down to the famil­iar level of aggrega­tive sta­tis­tics, or stock-​​and-​​flow continuous-​​valued sys­tems models.

Sub­jec­tively, when folks ask for some­thing so intrin­si­cally focused on story-​​telling to be “sim­pli­fied down to cleaner math”, it fees a lot like when old-​​school pro­gram­mers ask to use Inte­ger val­ues for Boolean val­ues (“-1 is false!”), or when I see sim­ple structs of prim­i­tives used instead of full-​​fledged objects in an object-​​oriented lan­guage. Some­thing about habits and famil­iar­ity, surely, but also an utterly dif­fer­ent sense of ele­gance and pur­pose, of craft, creep­ing in.

(Which is inter­est­ing, and worth watch­ing over time. Some­thing very sim­i­lar comes up when I read this.)

At any rate, a Boolean Net­work feels like a nice, tun­able model of a com­plex world with hid­den inter­nal struc­ture. In addi­tion to tun­able inter­nal com­plex­ity, one can always add exter­nal­i­ties, noise, struc­tural dynam­ics, all sorts of things that model the way we treat error and uncer­tainty in the real world much more authen­ti­cally than merely adding some normally-​​distributed epsilon to a number.

But there’s an inter­est­ing mod­el­ing choice before me, now, and I’m think­ing aloud about it. As you’ve read, I’ve sketched a world with use­ful tun­able para­me­ters; I’ve sketched a com­par­i­son (“water­fall” vs “agile” as vari­a­tions in tim­ing and order of staged work). But one does want one’s sim­u­lated “Team” to be able to do that work in a rea­son­able way.

So what is “require­ments gath­er­ing”? Or design, or cod­ing, or test­ing? As hap­pens now and then when build­ing com­plex sys­tems mod­els, the ques­tion is not “What do peo­ple really do?”, but rather, What is the sim­plest con­vinc­ing mimic of what is implied by a story in which we say, ‘Five require­ments have been gath­ered’? Or, Six­teen designs have been con­sid­ered, or Eleven tests have been cre­ated and run?

I have some notions, as you can see in my notes at GitHub. But there’s also this feel­ing that peo­ple brought up in the clas­si­cal math­e­mat­i­cal mod­el­ing world (the one that per­fuses com­puter sci­ence as well) will prob­a­bly raise their eye­brows. One is brought up to think of vari­ables as prim­i­tives, and of inter­ac­tions not as algo­rithms but as equa­tions. One is trained by decades of expen­sive com­put­ing and resource lim­i­ta­tion to assume that aggre­ga­tion takes place prop­erly within a model, using stocks and flows and aggrega­tive mea­sures and sta­tis­tics, deriv­a­tives and aver­ages all over—and not to see each instance or run of a model as being contingent.

This is a kind of pre­ma­ture opti­miza­tion that I haven’t heard remarked before. But I think it’s close to the core of what makes “com­plex­ol­ogy” abhor­rent unto the jour­nal­ist. And what’s inter­est­ing is that it’s com­ing from nerds who have almost cer­tainly dab­bled a bit with these alien, thrilling, com­plex­o­log­i­cal mod­els: imple­mented a Game of Life, for example.

And yet I think most haven’t real­ized that con­tin­gency and sub­jec­tiv­ity are baked right in. Pro­tip: On aver­age, over long time scales, all Game of Life runs are empty.

Maybe nobody’s pointed that out before. I think they prob­a­bly ought to have done so.