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Program to calculate root of cubics
https://forum.osdev.org/viewtopic.php?f=13&t=37031
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Author:  nullplan [ Wed Jul 22, 2020 11:27 am ]
Post subject:  Program to calculate root of cubics

Hi all,

had a bit of time on my hands and so I wrote something i wanted to implement for a while now, namely a program to calculate the roots of cubic expressions (by Cardano's method). Now I've written it, I am not entirely sure if I'm doing everything right. I added a check for the results at the end, and I regularly get results on the order of 1e-16. Is that entirely down to my non-optimized programming? Or did I get something wrong?

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File comment: source code
cubic.c [7.35 KiB]
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Author:  Octocontrabass [ Wed Jul 22, 2020 8:48 pm ]
Post subject:  Re: Program to calculate root of cubics

Double-precision values can accurately store around 15 decimal digits, so that sounds like normal rounding error.

By default, compilers don't change the order of floating-point operations while optimizing, so you may be able to improve the rounding error by changing how you calculate intermediate values.

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