Ask Your Question
0

TypeError for hom between multivariate Laurent polynomial rings?

asked 2015-05-12 11:47:39 -0500

Greg Muller gravatar image

updated 2015-10-16 12:19:59 -0500

FrédéricC gravatar image

I am having an error whenever I attempt to construct a homomorphism

  • from a Laurent polynomial ring

  • to a Laurent polynomial ring in more than one variable.

Ex (SageMath Cloud, 5/12/15):

R.<a>=LaurentPolynomialRing(ZZ)

S.<b,c>=LaurentPolynomialRing(ZZ)

phi=Hom(R,S)([b])

TypeError: images do not define a valid homomorphism

Additional data:

  • An identical error occurs with the variant syntax R.hom([b]).

  • An identical error occurs when trying to construct the identity homomorphism on LaurentPolynomialRing(ZZ,'x,y').

  • There is no error if the domain is replaced by PolynomialRing(ZZ,'a').

  • There is no error if the image of 'a' is 1.

  • There is no error if the codomain is replaced by its own fraction field.

It appears that Sage is incorrectly determining that the reciprocal of the image of the generator(s) is not in the codomain.

edit retag flag offensive close merge delete

Comments

I note that R.hom([b], check=False) works ok.

Francis Clarke gravatar imageFrancis Clarke ( 2015-05-15 04:54:46 -0500 )edit

1 answer

Sort by » oldest newest most voted
1

answered 2015-05-16 04:28:22 -0500

Francis Clarke gravatar image

It seems that the root of the problem is :

sage: R.<a> = LaurentPolynomialRing(ZZ)
sage: S.<b,c> = LaurentPolynomialRing(ZZ)
sage: a.is_unit()
True
sage: b.is_unit()
Traceback (most recent call last):
...
NotImplementedError:
edit flag offensive delete link more

Comments

Dang! I noticed even with your check=False workaround, I got a NotImplementedError when I tried to evaluate a map. How do I go about implementing it myself?

Greg Muller gravatar imageGreg Muller ( 2015-05-17 12:56:22 -0500 )edit

I just made a ticket about that : http://trac.sagemath.org/ticket/18465

FrédéricC gravatar imageFrédéricC ( 2015-05-21 05:05:24 -0500 )edit

Your Answer

Please start posting anonymously - your entry will be published after you log in or create a new account.

Add Answer

Question Tools

Stats

Asked: 2015-05-12 11:47:39 -0500

Seen: 70 times

Last updated: May 16 '15