> > Unfortunately, most models are not built atop fixed instruction sets. > Most models are built atop a very complicated stack of abstraction > layers, which means the effective number of "instructions" and terminals > (data types as well as values) is infinite. If we were building our > models in, say, assembly, I might agree with you. >
Actually assembly is the most versatile because it is ultimately what all computer languages have to target. Only when one has abstraction layers is there the _possibility_ of artificially limiting things (like saying that functions can't define functions). > >/ General > />/ and effective methods for global search can in fact be exactly the same > />/ for numbers and rules: 0) create a set of starting candidates 1) > />/ evaluate them, 2) tweak the good 3) destroy the bad, 4) go to 1. > / > You're playing language games. Yes, the methods _can_ be the same in > the extreme case you lay out. But, in fact they are NOT the same in > most cases. > Simulated annealing or genetic algorithms offer global optimization, whereas common quasi-Newton methods do not. The latter are merely efficient local optimizers and only handle simple landscapes. In any case, it doesn't really matter because both an operand and an operator can be encoded as a number (and are on real machines -- this encoding gives us all the software we use). Thus, `conventional' optimizers can in principle be used with operators. It's just that you probably wouldn't get anywhere because conventional optimizers can't handle non-linearity of ad-hoc functions, hard edges, etc. The rest of the practical considerations in doing search over sequences of operators are just that, e.g. for machine code one needs to trap exceptions and provide time limits on execution. > The source code is not the model, it's merely one of the > many generators for the model. //But I bet the midi-chlorians know where to find the whole thing. Marcus ============================================================ FRIAM Applied Complexity Group listserv Meets Fridays 9a-11:30 at cafe at St. John's College lectures, archives, unsubscribe, maps at http://www.friam.org
