POV-Ray : Newsgroups : povray.programming : solving polynomials : Re: solving polynomials Server Time
19 Sep 2021 15:45:59 EDT (-0400)
  Re: solving polynomials  
From: Le Forgeron
Date: 20 Oct 2016 14:02:44
Message: <580906c4@news.povray.org>
Le 20/10/2016 à 09:39, robfi680 a écrit :
> I was just looking at the source code for POVRay 3.7 for solving polynomials. In
> the default case for Solve_Polynomial it looks to me like it solves the
> polynomial twice for orders higher than four when a root is eliminated. I am
> trying to understand the code for my own use. Could there be a break statement
> missing ? Otherwise why does it solve for order n-1 and then n ?
> 
> The code looks like:
>   default:
> 
>    if (epsilon > 0.0)
>    {
>     if ((c[n-1] != 0.0) && (fabs(c[n]/c[n-1]) < epsilon))
>     {
>      Thread->Stats()[Roots_Eliminated]++;
> 
>      roots = polysolve(n-1, c, r);
>     }
>    }
> 
>    /* Solve n-th order polynomial. */
> 
>    roots = polysolve(n, c, r);
> 
>    break;
> 
> 
> 

The interesting part is that master branch is already corrected : yes, a
break is/was missing.

Now, it only occurs for 5th and more order polynomial, something that is
rarely seen.

The correction was done on 8th September 2016, found by static code
analysis.


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