Dear all, Currently one can obtain surprising results in Sage when converting polynomial over finite fields (or elements of quotient rings of univariate polynomial ring even though tht's not the primary concern of the ticket). See http://trac.sagemath.org/ticket/11239 Basically the generators of the finite fields are just exchanged, even when the characteristics are different. The changes suggested in this ticket would more or less only let a coercion be used if there is one, and rant if the characteristics are different or the base finite fields are not part of a common lattice when there is no canonical embedding.
Note though that the original disturbing conversion fits with the current behavior described in the doc: * http://www.sagemath.org/doc/reference/coercion/index.html#maps-between-parents where it's stated that "Conversions need not be canonical (they may for example involve a choice of lift) or even make sense mathematically (e.g. constructions of some kind)." Anyone has a strong opinion about what we should let Sage do in such a situation? Should we leave the old conversion when there is no coercion even though that might easily to wrong mathematical results for a careless user? Or never look for a coercion unless the user explicitly asks for it (i.e. what the situation is currently in Sage without the patches of the ticket)? Best, JP -- You received this message because you are subscribed to the Google Groups "sage-devel" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/sage-devel. For more options, visit https://groups.google.com/groups/opt_out.
