Greg Muller's profile - activity

2015-05-17 19:56:22 +0200	commented answer	TypeError for hom between multivariate Laurent polynomial rings? 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?
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2015-05-12 18:47:39 +0200	asked a question	TypeError for hom between multivariate Laurent polynomial rings? 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.