Re: wrong limit ?
- To: mathgroup at smc.vnet.net
- Subject: [mg76797] Re: wrong limit ?
- From: "David W.Cantrell" <DWCantrell at sigmaxi.net>
- Date: Sun, 27 May 2007 05:05:34 -0400 (EDT)
- References: <email@example.com>
ventu <nuclearVentu at gmail.com> wrote: > Hi ! > Here's my problem (mathematica 5.0,5.1,5.2): > > Limit[Coth[xB], B -> +Infinity] > > it doesn't understand. Having a space between x and B might have helped, but in fact the limit is then returned unevaluated in version 5.2. > mmh. ok I try then: > > Limit[Coth[x B], B -> +Infinity, Assumptions -> Im[x] == 0] > > 1 > > WRONG ! Yes, I think you discovered a bug. I wonder if it exists in version 6. > In fact: > > Limit[Coth[x B], B -> +Infinity, Assumptions -> Im[x] == 0 && Re[x] < 0] > > -1 > > Indeed the correct result should be sign(x). I presume you're talking about the correct result for Limit[Coth[x B], B -> Infinity, Assumptions -> Element[x, Reals]]. But no, Sign[x] would not be correct because Sign is 0, while the limit would be ComplexInfinity when x is 0. However, it would be nice if Limit[Tanh[x B], B -> Infinity, Assumptions -> Element[x, Reals]] gave Sign[x], rather than, incorrectly, 1. David W. Cantrell