Re: Limit Question

*To*: mathgroup at smc.vnet.net*Subject*: [mg66456] Re: [mg66452] Limit Question*From*: Andrzej Kozlowski <akoz at mimuw.edu.pl>*Date*: Sun, 14 May 2006 02:57:30 -0400 (EDT)*References*: <200605130642.CAA08939@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

On 13 May 2006, at 15:42, Blimbaum, Jerry CIV NSWC PC wrote: > > Why do these give no output? > > Simplify[Limit[Exp[-a t],t->Infinity],a>0] > > and same for > > Simplify[Limit[Exp[a t],t->Infinity],a<0] > > thanks... > > Jerry Blimbaum > > > Simplify will not help with Limit problems but Assumptions will: Limit[Exp[(-a)*t], t -> Infinity, Assumptions -> a > 0] 0 Limit[Exp[(-a)*t], t -> Infinity, Assumptions -> a < 0] Infinity The problem is that while Limit now accepts assumptions, unlike other functions that do so it does not (yet?) return conditional answers. Compare this with: Integrate[E^(-(a*t)), {t, 0, Infinity}] If[Re[a] > 0, 1/a, Integrate[E^((-a)*t), {t, 0, Infinity}, Assumptions -> Re[a] <= 0]] Simplify[%, a > 0] 1/a The only reason why Simplify worked below was that the answer to the previous output was returned in the form of a condition. Andrzej Kozlowski

**References**:**Limit Question***From:*"Blimbaum, Jerry CIV NSWC PC" <jerry.blimbaum@navy.mil>