Comment by lmm | Hacker News Reader

Comment by lmm | Hacker News Reader

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> analog computers don't generally compute by operating on symbols. For example see the classic video on fire control computers https://youtu.be/s1i-dnAH9Y4?t=496

> OP's specific phrasing is that they "map symbols to symbols". Analog computers don't do that. Some can, but that's not their definition.

How is that not symbolic? Fundamentally that kind of computer maps the positions of some rods or gears or what have you to the positions of some other rods or gears or what have you, and the first rods or gears are symbolising motion or elevation or what have you and the final one is symbolising barrel angle or what have you. (And sure, you might physically connect the final gear directly to the actual gun barrel, but that's not the part that's computation; the computation is the part happening with the little gears and rods in the middle, and they have symbolic meanings).

There's a confusion of nomenclature.

Computers are functional mappings from inputs to outputs, sure.

Analog fire computers are continuous mappings from a continuum, a line segment (curved about a cam), to another continuum, a dial perhaps.

Symbolic operations, mapping from patterns of 0s and 1s (say) to other patterns are discrete, countable mappings.

With a real valued electrical current, discrete symbols are forced by threshold levels.

To what degree is the threshold precise? Maybe fundamentally there's not that much difference.

> Analog fire computers are continuous mappings from a continuum, a line segment (curved about a cam), to another continuum, a dial perhaps.

> Symbolic operations, mapping from patterns of 0s and 1s (say) to other patterns are discrete, countable mappings.

What definition of "symbolic" are you using that draws a distinction between these two cases? If it means merely something that symbolises something else (as I would usually use it), then both a position on a line segment and a pattern of voltage levels qualify. If you mean it in the narrow sense of a textual mark, that pattern of voltage levels is just as much not a "symbol" as the position on the line segment.

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