On Apr 29, 4:04 pm, Tom Bachmann <[email protected]> wrote: > > Intuitively?! Oh, I see how I must have been misleading. I suppose I > > should have used a different syntax than what I used. But > > mathematically what is lim_{x,y->oo} x-y ? My impression is that if > > the order of the limit matters I would expect "undefined" as an > > answer. My intuition says that there isn't one variable going to > > infinity faster. If you assume one does, then you assume a particular > > answer. > > The following are three different mathematical concepts: > > lim(lim(f(x,y), x, oo), y, oo) > lim(lim(f(x,y), y, oo), x, oo) > lim_{x, y \to oo} f(x,y) <-- sympy does not have an expression for > this, and it wouldn't be implemented anyway > > As you have just discovered, in general these need not be the same > (and in fact you can even cook up examples where all limits involved > are finite). >
Yes, I now think it's right. x-y as x,y go to oo is undefined, but x-oo as x goes to oo is -oo. Having oo by itself in an expression is a weird concept, though. Julien -- You received this message because you are subscribed to the Google Groups "sympy" group. 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/sympy?hl=en.
