RE: RE: Absolute Value of Complex Numbers

*To*: mathgroup at smc.vnet.net*Subject*: [mg35221] RE: [mg35207] RE: [mg35196] Absolute Value of Complex Numbers*From*: "DrBob" <majort at cox-internet.com>*Date*: Wed, 3 Jul 2002 05:13:18 -0400 (EDT)*Reply-to*: <drbob at bigfoot.com>*Sender*: owner-wri-mathgroup at wolfram.com

The point is that ComplexExpand DOES assume k is a real number, while Abs, Simplify, and FullSimplify do not. You can cause Simplify to assume it, however: Simplify[Abs[2 Exp[k*I]], {Element[k, Reals]}] 2 However, you shouldn't use any of these tricks unless "k is Real" is a good assumption in your application. If not, Mathematica's original answer is correct. (In fact, it's correct regardless.) Bobby -----Original Message----- From: David Park [mailto:djmp at earthlink.net] To: mathgroup at smc.vnet.net Subject: [mg35221] [mg35207] RE: [mg35196] Absolute Value of Complex Numbers Kyle, You are assuming that k is a real number, but Mathematica doesn't assume that. Use ComplexExpand to Simplify. (Perhaps they should have called it ComplexSimplify.) Abs[2 Exp[k*I]] // ComplexExpand 2 David Park djmp at earthlink.net http://home.earthlink.net/~djmp/ > From: Kyle Davis [mailto:kyledavis at nowhere.com] To: mathgroup at smc.vnet.net > > Abs[2 Exp[3 * i]] > answer = 2 > > Abs[2 Exp[k * i]] > answer = 2 Exp[-Im[k]] > > Isn't the second answer supposed to be the same with the first one, > regardless with the value of k? How do I make the second > calculation give me > the right answer? > >