The problem may reside in the backtranslation of a Maxima result to Sage:
charpent@zen-book-flip:~$ sage
┌────────────────────────────────────────────────────────────────────┐
│ SageMath version 9.2.beta14, Release Date: 2020-09-30 │
│ Using Python 3.8.6. Type "help()" for help. │
└────────────────────────────────────────────────────────────────────┘
┏━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┓
┃ Warning: this is a prerelease version, and it may be unstable. ┃
┗━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┛
sage: var("k")
k
sage: assume(k<0)
sage: f=function("f")
sage: Eq=f(x).diff(x,2)/f(x)==k
sage: S=desolve(Eq, f(x), ivar=x); S
_K2*cosh(sqrt(k)*x) + I*_K1*sinh(sqrt(k)*x)
sage: SS=maxima.subst([sqrt(k)==I*sqrt(-k)], S); SS
_SAGE_VAR__K2*cos(sqrt(-_SAGE_VAR_k)*_SAGE_VAR_x)-_SAGE_VAR__K1*sin(sqrt(-_SAGE_VAR_k)*_SAGE_VAR_x)
sage: SS.sage()
# CRASH :
------------------------------------------------------------------------
/usr/local/sage-9/local/lib/python3.8/site-packages/cysignals/signals.cpython-38-x86_64-linux-gnu.so(+0x842b)[0x7fac8352242b]
# Etc. ad nauseam...
HTH,
Le jeudi 1 octobre 2020 à 17:36:50 UTC+2, Emmanuel Charpentier a écrit :
> 1) The problem also appears in sagecell <https://sagecell.sagemath.org/>,
> which contradicts my constatation of having done this yesterday…
>
> 2) The problem is *not* in Maxima:
>
> ;;; Loading #P"/usr/local/sage-9/local/lib/ecl/sb-bsd-sockets.fas"
> ;;; Loading #P"/usr/local/sage-9/local/lib/ecl/sockets.fas"
> Maxima 5.44.0 http://maxima.sourceforge.net
> using Lisp ECL 20.4.24
> Distributed under the GNU Public License. See the file COPYING.
> Dedicated to the memory of William Schelter.
> The function bug_report() provides bug reporting information.
> (%i1) display2d:false;
>
> (%o1) false
> (%i2) assume(k<0);
>
> (%o2) [k < 0]
> (%i3) Eq:diff(f(x),x,2)/f(x)=k;
>
> (%o3) 'diff(f(x),x,2)/f(x) = k
> (%i4) S:ode2(Eq,f(x),x);
>
> (%o4) f(x) = %i*%k1*sinh(sqrt(k)*x)+%k2*cosh(sqrt(k)*x)
> (%i5) subst([sqrt(k)=%i*sqrt(-k)],S);
>
> (%o5) f(x) = %k2*cos(sqrt(-k)*x)-%k1*sin(sqrt(-k)*x)
>
> HTH,
> Le jeudi 1 octobre 2020 à 16:59:58 UTC+2, Emmanuel Charpentier a écrit :
>
>> A new, interesting, and (IMHO) very serious bug :
>>
>> f=function("f")
>> var("k")
>> Eq=f(x).diff(x,2)/f(x)==k
>> with assuming(k>0):Sp=desolve(Eq,f(x),ivar=x)
>> with assuming(k==0):Sz=desolve(Eq,f(x),ivar=x)
>> with assuming(k<0):Sn=desolve(Eq,f(x),ivar=x)
>> var("_K1,_K2")
>> # with assuming(k<0): Sn1=Sn.subs(sqrt(k)==I*sqrt(abs(k))) # Crashes Sage
>> # with assuming(k<0): Sn2=Sn.subs(sqrt(k)==I*sqrt(-k)) # Crashes Sage also
>> # Maybe "with assuming..." fails ?
>> assume(k<0)
>> # Sn3=Sn.subs(sqrt(k)==I*sqrt(abs(k))) # Crash again
>> # Sn4=Sn.subs(sqrt(k)==I*sqrt(-k)) # Still crashes...
>>
>> Similar tricks *ejusdem farinae* worked up to 9.2.beta13… Did pynac
>> handling got modified ?
>>
>> What I get in a sage-shell-mode emacs session is in the attached
>> PynacCrash.txt (too long for the post body…). Advice on how to create an
>> informative ticket welcome...
>> .HTH,
>>
>>
>> Le jeudi 1 octobre 2020 15:57:03 UTC+2, Emmanuel Charpentier a écrit :
>>>
>>> ptestlong on a rebuilt 9.2.beta14+Trac#30675
>>> <https://trac.sagemath.org/ticket/30675>results in one transient and
>>> five permanent failures, partially different from those obtained on the
>>> same machine with 9.2.beta13 :
>>> File Result P/T
>>> src/sage/schemes/hyperelliptic_curves/monsky_washnitzer.py Killed due
>>> to abort P
>>> src/sage/tests/parigp.py Timed out T
>>> src/sage/modules/fg_pid/fgp_module.py 3 doctests failed P
>>> src/doc/en/constructions/algebraic_geometry.rst 1 doctest failed P
>>> src/doc/en/developer/coding_in_other.rst 1 doctest failed P
>>> src/sage/modules/free_module_morphism.py 3 doctests failed P
>>> HTH,
>>> Le jeudi 1 octobre 2020 à 01:22:01 UTC+2, Volker Braun a écrit :
>>>
>>>> As always, you can get the latest beta version from the "develop" git
>>>> branch. Alternatively, the self-contained source tarball is at
>>>> http://www.sagemath.org/download-latest.html
>>>>
>>>> Again, if there is anything that should be merged in this beta cycle
>>>> then a positively-reviewed patch has to materialize real soon ;-)
>>>>
>>>> 1da6df404d (tag: 9.2.beta14) Updated SageMath version to 9.2.beta14
>>>> be1a62b3bc Trac #30671: Random failure in src/sage/interfaces/psage.py
>>>> ed7c4a3ee0 Trac #30605: improve cone containment tests
>>>> ad0f8e0a1f Trac #30601: Move bitset.pxi to bitset_base.pxd
>>>> 89bf834ab3 Trac #30597: Define a sparse bitset structure
>>>> c539c2870a Trac #30663: tox.ini: Docker on Mac now needs $HOME too
>>>> 112d9daff1 Trac #30658: conda-forge-ubuntu-standard: Pillow fails to
>>>> install (follow up)
>>>> 0ef7e3ece8 Trac #30631: fix R on macOS xcode 12
>>>> 6576814c37 Trac #30603: Upgrade readline to 8.0
>>>> aa0a6d7b5f Trac #30546: python3 spkg-configure: Only search for
>>>> "python3", implement "configure --with-python=/PATH/TO/PYTHON"
>>>> 6969c604ad Trac #30664: Fixup for "Add quiet mode for bootstrap"
>>>> ebf4d9cf63 Trac #30662: Update conda package information, and fix
>>>> building Sage on conda
>>>> cbd8e5db72 Trac #29061: Upgrade to symmetrica-3.0.1
>>>> 99ab61da02 Trac #30596: Outsource functions in bitset.pxi that can be
>>>> optimized by intrinsics
>>>> 97802f668d Trac #30595: Remove deprecated sage.libs.ppl
>>>> 9ed2f32d19 Trac #30585: Typo ticket: homogenous -> homogeneous
>>>> 9c205e9694 Trac #30577: remove test file for python3 syntax
>>>> 0b841a75e6 Trac #30575: add maple conversion for hypergeometric
>>>> functions
>>>> de8e68e534 Trac #30572: Remove indirect typecasts when calling
>>>> bitset.pxi
>>>> dbd108c10b Trac #30567: remove deprecated things in words
>>>> b4715d1b68 Trac #30563: Use configuration variable MAXIMA instead of
>>>> hardcoding "maxima"
>>>> 865f3ca815 Trac #30562: Gap downloads from wrong upstream directory
>>>> cd88566df0 Trac #30548: mention that sometimes it is wolfram, not math
>>>> for Mathematica script
>>>> 7169ec9867 Trac #30547: full flake8 for skew_tableau.py, as an
>>>> experiment
>>>> 95712fc6ad Trac #30544: spkg-configure, system package info for tox
>>>> 2413f7b665 Trac #30523: polynomial_element.pyx: roots: SR: Fix if
>>>> determinant is not real
>>>> 28b594bb6e Trac #30486: Prepare doctests for Arb 2.18
>>>> 43089d428d Trac #30337: Graphs: obtain distance-regular graphs from
>>>> generalised quadrangles
>>>> 82a9e2d091 Trac #29500: Install all Python packages via pip wheel (or
>>>> setup.py bdist_wheel), store wheels in $SAGE_LOCAL/var/lib/sage/wheels
>>>> 85906ba097 Trac #25119: Fail to integrate sqrt(x^2)/x
>>>> 5bf821488c Trac #15223: Let the `TestSuite` test that the construction
>>>> of a parent returns the parent
>>>> 501019f5b5 Trac #30610: Fix openblas to build with Xcode 12
>>>> 19be84362c Trac #30576: Python 3.6: Fix locale/encoding issues in
>>>> docbuild, then re-enable Python 3.6
>>>> af71febd64 Trac #30008: After #30053, sphinx 3.1.2 does not build on
>>>> ubuntu-{trusty,xenial,bionic}, debian-jessie, centos-7 (again)
>>>> 82534f5b92 Trac #30538: some flake8 cleanup in manifolds
>>>> 3d4a8d2e75 Trac #30533: Add quiet mode for bootstrap
>>>> 8700f751cf Trac #30532: sage.rings.ideal: Do not import
>>>> sage.interfaces.singular at load time
>>>> 0957fb642a Trac #30526: Irrelevant Example for _polynomial_list at
>>>> FP_template.pxi
>>>> 3d4760ce77 Trac #30522: polynomial_element.pyx: roots: SR: Return value
>>>> for vanishing determinant broken
>>>> 2fd8ef799e Trac #30516: Infinite WeightedIntegerVectors does not coerce
>>>> properly
>>>> e3de8ecdfb Trac #30515: implement string formatting for elements in RR
>>>> and CC
>>>> 6844bbe72a Trac #30514: fix pycodestyle E701/E702 in combinat
>>>> 6b4b28b893 Trac #30513: fix pycodestyle E401
>>>> 7314b0db62 Trac #30510: Speed up method subgraph
>>>> 16b1089743 Trac #30509: Graphs: Faster implementation for HalfCube
>>>> 15cebad2f0 Trac #30503: src/tox.ini: Add environment codespell
>>>> 12c246ff72 Trac #30502: typo ticket 09/2020
>>>> 8543b383c8 Trac #30497: more lgtm-suggested fixed
>>>> 55568686a8 Trac #30493: bug in border case in highest weight vectors of
>>>> tensor product of crystals
>>>> 12aa127d55 Trac #30492: Provide conversion methods to remove
>>>> cythonizing from doctests
>>>> 49f3450dab Trac #29975: Make numerical and probability doctests ready
>>>> for random seeds
>>>> 055c07e8c6 Trac #28394: comparison of sage rationals with gmpy2 mpq
>>>> broken
>>>> e1a7af2252 Trac #26060: Wrong limit(x / (x + 2^x + cos(x)), x=-oo)
>>>> cd50ac9ea4 Trac #5178: Make LLL_gram also work with Gram matrices with
>>>> non-integer entries
>>>> 69c51603dd Trac #30583: Upgrade: gmpy2 2.1.0.b5
>>>> 6aa190cdee Trac #30531: Polyhedron_normaliz._triangulate_normaliz
>>>> should not use NmzResult directly
>>>> ff880f9919 Trac #29164: Computing log(0, 2) takes a long time
>>>> d55e6c9835 Trac #30604: fix scipy for XCode 12
>>>> 468f23815a (tag: 9.2.beta13) Updated SageMath version to 9.2.beta13
>>>>
>>>>
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