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From: "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com>
Newsgroups: sci.math
Subject: Re: Equation complexe
Date: Tue, 25 Feb 2025 14:00:01 -0800
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On 2/25/2025 1:49 PM, Chris M. Thomasson wrote:
> On 2/25/2025 6:23 AM, Richard Hachel wrote:
>> x^4=-81
>>
>> What is x?
> 
> 
> Try to forgive the floating point precision aspects, but, the roots are 
> the r's, raising them to the 4'th power gives the p's:
> _____________________
> r0 = (2.12132,2.12132)
> r1 = (-2.12132,2.12132)
> r2 = (-2.12132,-2.12132)
> r3 = (2.12132,-2.12132)
> 
> p0 = (-81,-7.08124e-06)
> p1 = (-81,-1.93183e-06)
> p2 = (-81,-7.53158e-05)
> p3 = (-81,4.57051e-05)
> _____________________
> 
> 
> To gain a root, here is my code:
> _____________________
> ct_complex
> root_calc(
>      ct_complex const& z,
>      int p,
>      int n
> ) {
>      float radius = std::pow(std::abs(z), 1.0 / p);
>      float angle_base = std::arg(z) / p;
>      float angle_step = (CT_PI * 2.0) / p;


>      float angle = angle = angle_step * n;
^^^^^^^^^^^^^^^^^^^^^^

It still compiles and works wrt C++, but this looks odd to me. I typed 
this in the newsreader just to see if I could remember it.

That line should be:

        float angle = angle_step * n;



> 
>      ct_complex c = {
>          std::cos(angle_base + angle) * radius,
>          std::sin(angle_base + angle) * radius
>      };
> 
>      return c;
> }
> _____________________
> 
> 
> Also, this is not using floating point for roots, just signed integers.