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pjeby comments on Without models - Less Wrong
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Perhaps my prolixity has obscured the substance. Here is a shorter version. The claims are:
1. The concept of a model is entirely unproblematic in this forum.
2. In that entirely unproblematic sense, neither a thermostat nor a cruise control contains a model.
3. The designer of a control system has a model. That model is located in the designer. He may or may not put a model into the system he designs. In the case of the thermostat and the cruise control, he does not.
I shall not repeat all of the evidence and argument, only summarise it:
1. Evidence was given in exhausting detail that I, and we on OB/LW, and the books all mean exactly the same thing by a model. Only in the threads on my two postings on control systems have some people tried to make it mean something different. But changing the definition is irrelevant to the truth-value of the original assertions. I think that no-one is disputing this now, although I shall not be surprised to see further expansions of the concept of a model. (I look forward to SilasBarta's promised article on the subject.)
2. Except for trivial models (one scalar "modelling" another) that leave out what the controller actually does (i.e. control something), there is nothing in either of these controllers but a simple rule generating its output from its inputs. That rule is not a model of something else. It acts upon the world, it does not model the world.
3. That the designer has a model is agreed by everyone. For some reason, though, when I say that the designer has a model, as I have done several times now, people protest that the designer has a model. We are in violent agreement. As for it being in his head, where else does he keep his thinking stuff? Well, "in his head" was not accurate, he might also make a computer simulation, or a physical mock-up. But when it comes time to build the actual system, what he builds is the actual system. The designer models the system; the system does not model the designer.
As for the appropriate form of my response, my judgement on that differs from yours. I shall stop at noting this meta-level disagreement.
From a computer programmer's perspective, a model is something that reflects the state of something else -- even a trivial single value like "the current temperature" or "the desired temperature".
If a thermostat only had a desired-temperature knob or only a "current temperature" indicator, I might agree that there's no model. A thermometer and a control knob don't "model" anything, in that there is nothing "reflecting" them. In the programming sense, there's no "view" or "controller".
But the moment you make something depend on these values (which in turn depend on the state of the world), it's pretty clear in programming terms that the values are models.