#5068: change_ring fails for polynomials over finite fields in many cases
----------------------+-----------------------------------------------------
Reporter: was | Owner: robertwb
Type: defect | Status: new
Priority: major | Milestone: sage-3.3
Component: coercion | Resolution:
Keywords: |
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Comment (by was):
The generic MPolynomial_polydict poly's work fine as looking at the code
shows, but the libsingular ones break:
{{{
sage: p = next_prime(10^30); f = GF(p^2,'a')['x,y'].gen()
sage: type(f)
<class
'sage.rings.polynomial.multi_polynomial_element.MPolynomial_polydict'>
sage: f.change_ring(GF(p))
x
sage: p = next_prime(20); f = GF(p^2,'a')['x,y'].gen()
sage: type(f)
<type
'sage.rings.polynomial.multi_polynomial_libsingular.MPolynomial_libsingular'>
sage: f.change_ring(GF(p))
---------------------------------------------------------------------------
TypeError Traceback (most recent call
last)
/Users/wstein/.sage/temp/teragon.local/22907/_Users_wstein__sage_init_sage_0.py
in <module>()
----> 1
2
3
4
5
/Users/wstein/build/sage-3.3.alpha0/local/lib/python2.5/site-
packages/sage/rings/polynomial/multi_polynomial.so in
sage.rings.polynomial.multi_polynomial.MPolynomial.change_ring
(sage/rings/polynomial/multi_polynomial.c:6691)()
661
662
--> 663
664
665
/Users/wstein/build/sage-3.3.alpha0/local/lib/python2.5/site-
packages/sage/rings/polynomial/multi_polynomial_libsingular.so in
sage.rings.polynomial.multi_polynomial_libsingular.MPolynomialRing_libsingular.__call__
(sage/rings/polynomial/multi_polynomial_libsingular.cpp:6267)()
616
617
--> 618
619
620
TypeError: unable to coerce <type
'sage.rings.finite_field_givaro.FiniteField_givaroElement'> to an integer
}}}
This is because the givaro finite field __call__ is wrong:
{{{
sage: GF(23)(GF(23^2,'a')(1))
BOOM!
TypeError: unable to coerce <type
'sage.rings.finite_field_givaro.FiniteField_givaroElement'> to an integer
but
sage: GF(next_prime(10^20))(GF(next_prime(10^20)^2,'a')(1))
1
}}}
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/5068#comment:1>
Sage <http://sagemath.org/>
Sage - Open Source Mathematical Software: Building the Car Instead of
Reinventing the Wheel
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