On Mon, Dec 17, 2012 at 6:10 PM, Benjamin Jones <benjaminfjo...@gmail.com> wrote: > > > 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
Sorry for the noise.. I meant to say (at the top) that from the implementation (of sage.symbolic.expression.Expression._mul_) it's pretty clear that this behavior *is* intentional, not a bug, but that's not to say it's desirable in all situations. -- 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.
