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Comment by turbobutton | Hacker News Reader

Having been downvoted, I like to clarify that this comes from the experience working in finance with developers with a strong academic background that emphasized on the necessity of formal proof to a point where complexity made actual progress nearly impossible- while simultaneously basing the proof repeatedly on assumptions that did not uphold in practice.

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Nah I don't disagree with you. Thing is even if you formally prove that for every input you produce a valid output. In safety certified software, there's the problem that if that input comes from a sensor, a sensor is an inherently probabilistic thing, and it may be that you will have false positives. The best you can do is build a safety case that even if you get false positives you end up in a safe state, but you can't guarantee that they won't ever increase operational costs.

I once had a sensor that rounded the data, so the output unwittingly fitted into a grid. The equations that had to be used on that data gave infinite results because the grid sometimes rounded slopes into vertical lines.

So I had to reconstruct a signal that fitted the data for the equations to work at all. But the reconstruction was no longer measured data. It was made up, and there was no single solution for fitting the data. That meant I could claim to "respect the data" while producing any result I wanted.

Reminds me of that von Neumann quote "With four parameters I can fit an elephant, and with five I can make him wiggle his trunk."

> "With four parameters I can fit an elephant, and with five I can make him wiggle his trunk."

Indeed: here are two papers on this topic:

Jürgen Mayer; Khaled Khairy; Jonathon Howard. Drawing an elephant with four complex parameters. 2010. https://pubs.aip.org/aapt/ajp/article-abstract/78/6/648/1042... Article without paywall : https://publications.mpi-cbg.de/Mayer_2010_4314.pdf

Dian Jin; Junze Yuan. Fitting an Elephant with Four non-Zero Parameters. 2024. https://arxiv.org/abs/2407.07909v1

Given that information can be encoded in a string of digits of infinite length, there is no limit to how precisely the elephant can be drawn. Any image file is a string of bits, a single parameter.

In cases like that you also will generally have three (or some odd number) of sensors and require a majority of them to agree to determine what your input is. Still not guaranteed to be correct, but the odds are better.

“3 B’s make a D” :D

what were some categories of such assumptions, can you name some examples?

a fun one that immediately comes to mind is asserting something holds for reals, but not evaluating whether it holds for IEEE floats, though maybe that's not really a thing in finance due to rounding related rules anyways

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