I'm not looking for a workaround. I know it happens. I can watch out for it.
I am really hoping that there is an improvement to make Sage behave better. Sage should be a good Computer Algebra System, but for examples like this it really pretty poor. Moreover, I am sure that other users will run into this same example and perhaps not notice that the coefficients 1 are disappearing (because in the case I first ran into it, the output was pages long). Let me give you another example of how I think Sage is not good at being a CAS: sage: (q,t)=QQ['q','t'].fraction_field().gens() sage: a = (-q^5)/(-t^3) sage: expand(a) (-q^5)/(-t^3) sage: simplify(a) (-q^5)/(-t^3) How do I get Sage to realize the output is not "right"? There is correct output and there is output which is helpful. Sage does the former very well, I think that there should be some effort put in the latter. -Mike On Friday, 17 April 2015 17:36:23 UTC-4, Travis Scrimshaw wrote: > > Hey Mike, > At least as a workaround you could do something like this: > > sage: s=SymmetricFunctions(QQ).s() > sage: x = s[2,1] + 2*s[3] > sage: for i,c in x: print i, factor(c) > [3] 2 > [2, 1] 1 > > Best, > Travis > > > On Wednesday, April 15, 2015 at 5:00:18 PM UTC-4, Mike Zabrocki wrote: >> >> Hi all, >> There is very strange behavior if you want factored coefficients of a >> free module. Let me give an example in the ring of symmetric functions: >> >> sage: s=SymmetricFunctions(QQ).s() >> sage: (s[2,1] + 2*s[3]).map_coefficients(factor) >> 2*s[3] >> >> What is happening here is that 'factor' returns a factorization object. >> factor(1) is an empty list and hence is 'false'. Now if you look at the >> code for 's._from_dict' it removes objects which are empty. >> >> If you look at the documentation for 'map_coefficients' you can see that >> this is not technically a bug because map_coefficients needs to be an >> endofunction on the coefficient ring. In this case, factor is mapping from >> QQ to factor objects and so I wouldn't want to play with the result of that >> command. On the other hand, in symmetric functions (especially with >> multiple parameters like Macdonald or Hall-Littlewood) one would frequently >> like to factor coefficients to know that the coefficients have a nice form. >> >> Does anyone have any suggestions about what should happen with this case? >> I was discussing it with a few people, but we ruled out changing >> factor, map_coefficients or _from_dict. >> >> I find that to work with coefficients in a polynomial ring, the functions >> factor, simplify, expand are unsatisfactory because the output is rarely in >> a form that shows me what I want to see (Maple and Mathematica seem better >> at this). Perhaps what I would like to have is a function 'niceify' that >> displays a coefficient in a pretty form. >> > -- You received this message because you are subscribed to the Google Groups "sage-combinat-devel" group. To unsubscribe from this group and stop receiving emails from it, send an email to sage-combinat-devel+unsubscr...@googlegroups.com. To post to this group, send email to sage-combinat-devel@googlegroups.com. Visit this group at http://groups.google.com/group/sage-combinat-devel. For more options, visit https://groups.google.com/d/optout.
