Re: "analog computer" = useless hypothesis?

From: Samantha (
Date: Tue Apr 03 2001 - 18:19:04 MDT

Jim Fehlinger wrote:
> I see your point, but you are overstating the case to an almost ludicrous
> degree. I'm responsible for debugging and maintaining one corner
> of an enormously complex ERP system with thousands of users. I've seen all the
> situations you mention (though I've never seen anything that was ultimately blamed on
> sunspots!), and all that stuff has to be sorted through and ruled out
> systematically when there's a problem. That's what programmers and system
> administrators and database administrators and network administrators and
> hardware techs get paid the big bucks for. Generally, one **doesn't** get
> away with claiming a bug is not reproducible (unless it's a very minor
> bug indeed!) -- all that means, from management's point of view, is that you
> haven't done enough work yet.

While I agree that there are no ghosts in the machine I absolutely
disagree that you can always, in finite time, reproduce any bug that
anyone has ever encountered in using a particular batch of code. There
are simply too many possible variables. Now, it is possible to build in
enough checking to catch most really anomalous situations more or less
gracefully. But even this is not necessarily sufficient as bugs
sometimes are in the subtle interaction of quite a number of components
all of which perfectly meet their contract as specified. Even properly
stating some of the interactions between components (especially in the
presence of callbacks) is not a very thoroughly mastered or even
altogether tractable task.

That computers are predictable no more means that you can predict in
practice everything they will ever do than in practice you can
successfully predict everything that will occur in nature even with a
TOE. The problem is just not computationally tractable beyond a certain

Determinism != Full Predictability in practice.

- samantha

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