[GiNaC-list] factorization bug

[Ivan Vasilyev]

Hi! I believe there's an intermittent bug in GiNaC::factor() function.
Sometimes it leaves uncancelled terms with seemingly random coefficients
like:

w*(w^2*(K^4*B^2+B^2-2*K^2*B^2)+196*w^2*K^4+196*w^2+C^2-196*w^2*(1+K^4-2*K^2)-392*w^2*K^2)*A

The minimal code to reproduce the bug in GiNaC 1.8.2 is:

#include <ginac/ginac.h>
#include <iostream>

int main()
{
    std::string input("w^3*B^2*A-2*w^3*K^2*B^2*A+w*C^2*A+w^3*K^4*B^2*A");
    while (true)
    {
        std::ostringstream s;
        GiNaC::parser reader;
        s << factor(reader(input));
        if (s.str().length() <= input.length())
            continue;
        std::cout << s.str() << '\n';
        return 0;
    }
}

Also, this problem can be reproduced on
https://daninet.github.io/ginac-wasm/ with the same expression being
calculated several times in a row:

factor(w^3*B^2*A-2*w^3*K^2*B^2*A+w*C^2*A+w^3*K^4*B^2*A);

With best regards,
Ivan.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.ginac.de/pipermail/ginac-list/attachments/20220131/dc8c1f63/attachment.htm>