On Sep 21, 9:26 am, Brandy Benedict <[email protected]> wrote: > Hi, > > I'm confused about the results I'm getting when I evaluate some limits > with Sage. For example, I want to find the limit of f(x)=2x/(x-3) as > x approaches 3. So I compute the one-sided limits with Sage, which > work perfectly: > > limit((2*x)/(x-3),x=3,dir='plus') {Gives output +Infinity} > > limit((2*x)/(x-3),x=3,dir='minus') {Gives output -Infinity} > > But, if I give Sage this command: > > limit((2*x)/(x-3),x=3) > > it gives me Infinity as output (with no sign). Why doesn't Sage tell > me that the limit doesn't exist?
Hi Brandy! Say hi to the other end of Route 114 for me... This is not clear in the documentation of sage: limit? It turns out that Infinity is Sage-speak for an "unsigned infinity". That is to say, as Winston Churchill put it, we see "a quantity passing through infinity and changing its sign from plus to minus." After all, technically speaking, the one-sided limits also don't exist. However, there is some inconsistency; see http://trac.sagemath.org/sage_trac/ticket/9480 And I agree that this is not well documented, though your example is essentially in the "TESTS" section (without explanation). I hope this at least explains what the output means! Best, - kcrisman -- To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/sage-support URL: http://www.sagemath.org
