On Apr 29, 2:17 pm, Ronan Lamy <[email protected]> wrote: > I would argue that the correct results are limit(x - oo, x, oo) == -oo > and limit(oo - x, x, oo) == oo. > > The expression whose limit is taken belongs to the extended real line, > so we need to consider the topology of the extended real line. Unless > otherwise specified, limits are always evaluated for values of the > variable close to, but different from, the "destination". In this case, > this means arbitrarily large, but finite, reals. For any real x, x - oo > = -oo, so the function Lambda(x, x - oo) is constant over the reals, but > discontinuous, undefined actually, at x = +oo. However, the latter > doesn't matter for the limit, and the result is the constant value, -oo. > All this is completely parallel to limit(abs(x)/x, x, 0, '+'), for > instance.
Take f(x,y)=x-y. By your account lim(lim(f(x,y),y,oo),x,oo) == -oo but lim(lim(f(x,y),x,oo),y,oo) == oo. This can't be right. -- 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.
