[GiNaC-list] matrix::solve()-related problems

[Richard B. Kreckel]

Hi,

On 28.01.2018 19:35, Alexey Sheplyakov wrote:
> 27.01.2018, 02:42, "Vitaly Magerya" <vmagerya at gmail.com>:
>  
>> These segfaults have this sort of backtrace:
>>
>> #1 0x00007ffff7a07f79 in GiNaC::ex::construct_from_basic(...)
>> #2 0x00007ffff79e19e2 in GiNaC::basic::subs_one_level(...) const
>> #3 0x00007ffff7b3d235 in GiNaC::power::subs(...) const
>> #4 0x00007ffff7a0ba11 in GiNaC::expairseq::subschildren(...) const
>> #5 0x00007ffff7a0bd64 in GiNaC::expairseq::subs(...) const
>> #6 0x00007ffff7a08d4e in GiNaC::ex::subs(...) const
>> #7 0x00007ffff7aeb6c0 in GiNaC::gcd(...)
>> #8 0x00007ffff7aea806 in GiNaC::gcd_pf_pow(...)
>> #9 0x00007ffff7aebbd0 in GiNaC::gcd(...)
>> #10 0x00007ffff7aeac26 in GiNaC::gcd_pf_pow(...)
>> #11 0x00007ffff7aebbd0 in GiNaC::gcd(...)
>>
>> (repeat the last two lines a whole bunch of times)
>>
>> #20147 0x00007ffff7aebbd0 in GiNaC::gcd(...)
>> #20148 0x00007ffff7aeac26 in GiNaC::gcd_pf_pow(...)
>> #20149 0x00007ffff7aea2f8 in GiNaC::gcd_pf_pow(...)
>  
> Looks like gcd() goes to an infinite recursion. Could you please make a
> breakpoint in
> GiNaC::gcd_pf_pow and print expressions which cause this misbehavior?

Well, it's not an infinite recursion.

But computations like gcd(expand(x^1000*(1+x)^2),x^1000) cause GiNaC to
recurse so deeply that it eventually overflows the stack. Also, they
take way too long. They appear a lot in Vitaly's example.

This goofy recursion ought to be shortcut, somehow.

   -richy.