On Monday, September 29, 2014 7:44:35 AM UTC-7, Volker Braun wrote: > > We talked about this once, afair it is the same in Magma. >
Except that in magma the print name of variables has no semantic value and can be changed at any point. > Really, there is no reason for forbidding it > Well, there is sage: R.<x,x,x>=QQ[] sage: SR(R.0+R.1) #good! at least we get an error TypeError: sage: maxima_calculus(R.0+R.1) 2*x sage: (R.0+R.1)._singular_() 2*x sage: (R.0+R.1)._singular_()._sage_() ValueError: variable names must be alphanumeric, but one is '@(2)' which is not. sage: (R.0+R.1)._pari_() 2*x sage: (R.0+R.1)._pari_()._sage_() #this is just a general bug; it happens for any poly. NameError: name 'x' is not defined > And deep inside your own code you might want to add a variable to a > polynomial ring given to you by the user, and it would be inconvenient to > have to pick a letter that is not yet present in the user input. > > I agree with that, although I would expect this is more important for things like QQ['x','y']['x'], where the clash as noted above would only manifest itself at a later stage if one tries to flatten the polynomial ring tower). The end result is that sage in principle should be able to handle such polynomial rings, but because it's a scenario people will not normally count on, and does need some extra care, so in practice there will always be bugs arising around this--hopefully failures, but as you can see above, possibly wrong results. I'm not quite sure what we should do with a misfeature like this. For orthogonality it is nice to not put any non-local restrictions on variable names, but it seems we don't have the infrastructure to enforce that such objects keep behaving reasonably. -- 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 sage-devel+unsubscr...@googlegroups.com. To post to this group, send email to sage-devel@googlegroups.com. Visit this group at http://groups.google.com/group/sage-devel. For more options, visit https://groups.google.com/d/optout.
