SEGV using algebraic_closure(QQ) #5648
Description
Describe the bug
An apparently harmless computation leads to SEGV after quite a long time; I'm not certain, but do not believe that it is caused by exhaustion of RAM/swap. The computation is not important to me: I was just playing with OSCAR
Here is what the error message was:
[560384] signal (11.1): Segmentation fault
in expression starting at REPL[13]:1
unknown function (ip: 0x7f2f08e4fb45)
flint_parallel_do at /home/zez25zuh/.julia/artifacts/f1fbaa2f3bc028c94a47175c5481b8e241352d3c/lib/libflint.so (unknown line)
_fmpz_vec_set_fft at /home/zez25zuh/.julia/artifacts/f1fbaa2f3bc028c94a47175c5481b8e241352d3c/lib/libflint.so (unknown line)
_fmpz_poly_mullow_SS at /home/zez25zuh/.julia/artifacts/f1fbaa2f3bc028c94a47175c5481b8e241352d3c/lib/libflint.so (unknown line)
_fmpq_poly_mullow at /home/zez25zuh/.julia/artifacts/f1fbaa2f3bc028c94a47175c5481b8e241352d3c/lib/libflint.so (unknown line)
_fmpq_poly_div_series at /home/zez25zuh/.julia/artifacts/f1fbaa2f3bc028c94a47175c5481b8e241352d3c/lib/libflint.so (unknown line)
fmpq_poly_div_series at /home/zez25zuh/.julia/artifacts/f1fbaa2f3bc028c94a47175c5481b8e241352d3c/lib/libflint.so (unknown line)
qqbar_fmpz_poly_composed_op at /home/zez25zuh/.julia/artifacts/f1fbaa2f3bc028c94a47175c5481b8e241352d3c/lib/libflint.so (unknown line)
qqbar_binary_op at /home/zez25zuh/.julia/artifacts/f1fbaa2f3bc028c94a47175c5481b8e241352d3c/lib/libflint.so (unknown line)
qqbar_add at /home/zez25zuh/.julia/artifacts/f1fbaa2f3bc028c94a47175c5481b8e241352d3c/lib/libflint.so (unknown line)
add! at /home/zez25zuh/OSCAR/GIT/Nemo.jl/src/calcium/qqbar.jl:1328
add! at /home/zez25zuh/OSCAR/GIT/AbstractAlgebra.jl/src/fundamental_interface.jl:406 [inlined]
fflu! at /home/zez25zuh/OSCAR/GIT/AbstractAlgebra.jl/src/Matrix.jl:1934
det_fflu at /home/zez25zuh/OSCAR/GIT/AbstractAlgebra.jl/src/Matrix.jl:2385
det at /home/zez25zuh/OSCAR/GIT/AbstractAlgebra.jl/src/Matrix.jl:2394
[...]
Allocations: 44910475 (Pool: 44830692; Big: 79783); GC: 16836
Segmentation fault (core dumped)
To Reproduce
Steps to reproduce the behavior, please provide a code snippet that triggers
the bug.
using Oscar
QQbar = algebraic_closure(QQ);
Kx,x = QQbar["x"];
N = 8;
f = x^N - (N^N*x-1)^2; # has 2 real roots close to N^(-N)
r = roots(f); # is the order of the result always the same?
r[2] - r[3] # the roots are close
M = matrix(QQbar,2,2,[r[1], r[2], r[5], r[6]+r[7]]);
display(M);
D = det(M) # quick
D^2 # also quick
M2 = M^2; # entries are in much-higher degree extensions
det(M2) # very slow -- then SEGV
Expected behavior
No SEGV
System (please complete the following information):
Please paste the output of Oscar.versioninfo(full=true) below. If this does
not work, please paste the output of Julia's versioninfo() and your Oscar
version.
julia> Oscar.versioninfo(full=true)
OSCAR version 1.7.0-DEV - #master, a3f6b0db86 -- 2025-12-10 10:15:35 +0100
combining:
AbstractAlgebra.jl v0.47.5 - #master, 811e27c103 -- 2025-12-10 13:43:02 +0000
GAP.jl v0.16.2
Hecke.jl v0.39.4 - #master, 2aee9450a4 -- 2025-12-09 19:57:26 +0100
Nemo.jl v0.53.0 - #master, 8e3aea0d7a -- 2025-12-01 17:26:42 +0100
Polymake.jl v0.13.4
Singular.jl v0.28.3
building on:
FLINT_jll v301.400.1+0
GAP_jll v400.1500.100+1
GAP_lib_jll v400.1500.100+0
Singular_jll v404.101.503+0
libpolymake_julia_jll v0.14.4+0
libsingular_julia_jll v0.47.9+0
polymake_jll v400.1500.1+0
polymake_oscarnumber_jll v0.3.13+0
See `]st -m` for a full list of dependencies.
Julia Version 1.10.10
Commit 95f30e51f41 (2025-06-27 09:51 UTC)
Build Info:
Official https://julialang.org/ release
Platform Info:
OS: Linux (x86_64-linux-gnu)
CPU: 20 × Intel(R) Core(TM) i9-10900 CPU @ 2.80GHz
WORD_SIZE: 64
LIBM: libopenlibm
LLVM: libLLVM-15.0.7 (ORCJIT, skylake)
Threads: 1 default, 0 interactive, 1 GC (on 20 virtual cores)
Environment:
JULIA_LOAD_PATH = @:@v#.#:@stdlib:/environments/globalenv
JULIA_DEPOT_PATH = /home/zez25zuh/.julia:
Official https://julialang.org/ release
Additional context
I'll try running with non DEV version of OSCAR, but expect the behaviour to be the same.