Doctest: segmentation fault with coefficients() on symbolic expressions

[Vincent Delecroix]

On sage 8.0

sage: (x^2/(1+x)).coefficients()
Segmentation fault (core dumped)

gdb shows that this is an infinite recursion in the Pynac library:

#0  GiNaC::add::integer_content (this=0x4095f00) at normal.cpp:95
#1  0x00007fff50051660 in GiNaC::ex::integer_content (this=this@entry=0x7fffff7ff410) at normal.cpp:81
#2  0x00007fff50076fdc in GiNaC::power::eval (this=0x7fffff800040, level=<optimized out>) at power.cpp:674
#3  0x00007fff4ff9b29e in GiNaC::ex::construct_from_basic (other=...) at ex.cpp:691
#4  0x00007fff50041ac3 in ex (other=..., this=0x7fffff800030) at ex.h:305
#5  GiNaC::mul::combine_ex_with_coeff_to_pair (this=0x40961a0, e=..., c=...) at mul.cpp:1228
#6  0x00007fff4ffa3084 in GiNaC::expairseq::evalchildren (this=this@entry=0x40961a0, level=1) at expairseq.cpp:1647
#7  0x00007fff50047390 in GiNaC::mul::eval (this=0x40961a0, level=<optimized out>) at mul.cpp:666
#8  0x00007fff4ff9b29e in GiNaC::ex::construct_from_basic (other=...) at ex.cpp:691
#9  0x00007fff50049ff6 in ex (other=..., this=0x7fffff800690) at ex.h:305
#10 GiNaC::mul::expand (this=0x4096030, options=0) at mul.cpp:1490
#11 0x00007fff4ff9ac0d in GiNaC::ex::expand (this=this@entry=0x7fffff800bf0, options=options@entry=0) at ex.cpp:84
#12 0x00007fff4ff9eec9 in expand (options=0, thisex=...) at ex.h:701
#13 GiNaC::match_monom (term=..., symb=..., vec=..., map=...) at ex.cpp:523
#14 0x00007fff4ff9f8c8 in GiNaC::ex::coefficients (this=this@entry=0x7fffff800e00, s=..., vec=...) at ex.cpp:576
#15 0x00007fff4ff9eed7 in GiNaC::match_monom (term=..., symb=..., vec=..., map=...) at ex.cpp:523
#16 0x00007fff4ff9f8c8 in GiNaC::ex::coefficients (this=this@entry=0x7fffff8011c0, s=..., vec=...) at ex.cpp:576
#17 0x00007fff4ff9eed7 in GiNaC::match_monom (term=..., symb=..., vec=..., map=...) at ex.cpp:523
#18 0x00007fff4ff9f8c8 in GiNaC::ex::coefficients (this=this@entry=0x7fffff801580, s=..., vec=...) at ex.cpp:576
#19 0x00007fff4ff9eed7 in GiNaC::match_monom (term=..., symb=..., vec=..., map=...) at ex.cpp:523
#20 0x00007fff4ff9f8c8 in GiNaC::ex::coefficients (this=this@entry=0x7fffff801940, s=..., vec=...) at ex.cpp:576
[...]

[Ralf Stephan]

Confirmed. I added a minimal case.

[Ralf Stephan]

The Pynac code does not check if the expression is a polynomial fraction in x. That case cannot be handled via coefficient() (the user should expand as a series). I will add a check to prevent this problem.

[Ralf Stephan]

Pynac master has the fix. This branch adds doctests.

---

New commits:

​617a644

23545: segmentation fault with coefficients() on symbolic expressions

[Ralf Stephan]

While the core dump is fixed in develop, one of the doctests fails.

[Emmanuel Charpentier]

Fixed by #24262. I will give positive review if necessary, but as suggest to matk it duplicate and close it (after positive review of #24262, pf course...)..

[Ralf Stephan]

This ticket has doctests for #24147 too so let's make #24147 the duplicate.

[Travis Scrimshaw]

LGTM.