SAGE ignores Ctrl-C?!? Is this a bug or a feature

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Alex P

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Dec 30, 2009, 12:37:19 AM12/30/09
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Here is the code:

----------------------------------------------------------------------
| Sage Version 4.2.1, Release Date: 2009-11-14 |
| Type notebook() for the GUI, and license() for information. |
----------------------------------------------------------------------
sage: q = 3
sage: F.<a> = FiniteField(q)
sage: P.<T> = PolynomialRing(F)
sage: PP.<z> = PolynomialRing(P)
sage: time (z + 1)^81
CPU times: user 0.17 s, sys: 0.00 s, total: 0.17 s
Wall time: 0.17 s
z^81 + 1
sage: time (2*z + 1)^81
CPU times: user 0.17 s, sys: 0.00 s, total: 0.17 s
Wall time: 0.17 s
2*z^81 + 1
sage: time (2*T*z + 1)^81
CPU times: user 0.17 s, sys: 0.00 s, total: 0.18 s
Wall time: 0.18 s
2*T^81*z^81 + 1
sage: time (z^3 + T*z)^81
CPU times: user 1.00 s, sys: 0.00 s, total: 1.00 s
Wall time: 1.00 s
z^243 + T^81*z^81
sage: time (z^3 + T*z)^(81*3)
CPU times: user 6.49 s, sys: 0.03 s, total: 6.51 s
Wall time: 6.51 s
z^729 + T^243*z^243
sage: time (z^3 + T*z)^(3^6)
CPU times: user 71.92 s, sys: 0.06 s, total: 71.98 s
Wall time: 72.38 s
z^2187 + T^729*z^729
sage: time (z^3 + T*z)^(3^7)
^CException KeyboardInterrupt: KeyboardInterrupt() in
'sage.rings.polynomial.polynomial_zmod_flint.get_cparent' ignored
^C

------------------------------------------------------------
Unhandled SIGFPE: An unhandled floating point exception occured in
SAGE.
This probably occured because a *compiled* component
of SAGE has a bug in it (typically accessing invalid memory)
or is not properly wrapped with _sig_on, _sig_off.
You might want to run SAGE under gdb with 'sage -gdb' to debug this.
SAGE will now terminate (sorry).
------------------------------------------------------------

Simon King

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Dec 30, 2009, 6:07:42 AM12/30/09
to sage-support
Hi Alex!

On 30 Dez., 06:37, Alex P <alexvpetr...@gmail.com> wrote:
> Here is the code:
>
> ----------------------------------------------------------------------
> | Sage Version 4.2.1, Release Date: 2009-11-14                       |
> | Type notebook() for the GUI, and license() for information.        |
> ----------------------------------------------------------------------
> sage: q = 3
> sage: F.<a> = FiniteField(q)
> sage: P.<T> = PolynomialRing(F)
> sage: PP.<z> = PolynomialRing(P)

[...]


> sage: time (z^3 + T*z)^(3^7)
> ^CException KeyboardInterrupt: KeyboardInterrupt() in
> 'sage.rings.polynomial.polynomial_zmod_flint.get_cparent' ignored
> ^C
>
> ------------------------------------------------------------
> Unhandled SIGFPE: An unhandled floating point exception occured in
> SAGE.
> This probably occured because a *compiled* component
> of SAGE has a bug in it (typically accessing invalid memory)
> or is not properly wrapped with _sig_on, _sig_off.
> You might want to run SAGE under gdb with 'sage -gdb' to debug this.
> SAGE will now terminate (sorry).
> ------------------------------------------------------------

That's certainly a bug. I created a ticket for it:
http://trac.sagemath.org/sage_trac/ticket/7794

As it is defined, PP is a polynomial ring in one variable over a
polynomial ring in one variable.
Would it be a good thing to automatically convert this into a
polynomial ring with *two* variables? What do people think? If you
have an opinion about it, you might also comment on
http://trac.sagemath.org/sage_trac/ticket/7580, where I do those
conversions for Infinite Polynomial Rings.

Note that Alex' example reveals another bug, this time in
MPolynomialRing_libsingular:
sage: F.<a> = FiniteField(3)
sage: P.<T,z> = PolynomialRing(F)
sage: type(P)
<type
'sage.rings.polynomial.multi_polynomial_libsingular.MPolynomialRing_libsingular'>
sage: (z^3 + T*z)^(81*3) # immediate answer
z^729 + T^243*z^243
sage: (z^3 + T*z)^(2^20)
/home/king/SAGE/sage-4.3/local/bin/sage-sage: line 206: 20889
Segmentation fault sage-ipython "$@" -i

This was without Ctrl-C.

Certainly there should be no segfault. If anything, there should an
error be raised.
I made this another ticket, http://trac.sagemath.org/sage_trac/ticket/7795

Thanks for the report!
Simon

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