On Mon, Dec 17, 2012 at 5:32 PM, Travis Scrimshaw <tsc...@ucdavis.edu>wrote:
> Hey Sebastien, > > But not for multiplication by a negative number : >> >> sage: - (x > 100) >> -x > -100 >> >> Do you consider this to be a bug? I would prefer the answer "-x < -100" >> to preserve the space of solutions. Do you? >> >> > The result is not what I would expect. However, I will let someone more > versed with the symbolic ring officially call it a bug. > > It's also not just negation, but honest multiplication: > > sage: (-1)*(x > 100) > -x > -100 > sage: ZZ(-1)*(x > 100) > -x > -100 > sage: SR(-1)*SR(x > 100) > -x > -100 > > Best, > Travis > > > -- > You received this message because you are subscribed to the Google Groups > "sage-devel" group. > To post to this group, send email to sage-devel@googlegroups.com. > To unsubscribe from this group, send email to > sage-devel+unsubscr...@googlegroups.com. > Visit this group at http://groups.google.com/group/sage-devel?hl=en. > > > It's hard to tell from the implementation if this behavior is intentional, unintentional, or a bug. The implementation is just that multiplication maps over relational operators like ==, <, <=, etc. But I think it's not possible in the current framework to make multiplication preserve the truth of a statement, e.g. if y > 0 is true, is x*(y > 0) true or false? You can't decide unless you know more about x. If you want to make multiplying by elements in SR preserve truth of a statement you have to decide this. The same question has come up on ask.sagemath: http://ask.sagemath.org/question/1656/multiplying-an-inequality-by-1 -- Benjamin Jones -- You received this message because you are subscribed to the Google Groups "sage-devel" group. To post to this group, send email to sage-devel@googlegroups.com. To unsubscribe from this group, send email to sage-devel+unsubscr...@googlegroups.com. Visit this group at http://groups.google.com/group/sage-devel?hl=en.
