Re: Limit Question

*To*: mathgroup at smc.vnet.net*Subject*: [mg66458] Re: Limit Question*From*: "David W. Cantrell" <DWCantrell at sigmaxi.org>*Date*: Sun, 14 May 2006 02:57:35 -0400 (EDT)*References*: <e43vun$90e$1@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

"Blimbaum, Jerry CIV NSWC PC" <jerry.blimbaum at navy.mil> 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] I must guess that it's because: 1. Limit[Exp[a t],t->Infinity] itself cannot be evaluated since the sign of a is not known. and 2. Simplify doesn't manage to get the necessary information about the sign of a inside Limit. In any event, here's an alternative that does work: In[10]:= Assuming[a>0, Limit[Exp[-a t], t->Infinity]] Out[10]= 0 In[11]:= Assuming[a<0, Limit[Exp[a t], t->Infinity]] Out[11]= 0 Apparently, Assuming does manage to get the necessary information about the sign of a inside Limit. Regards, David