Re: Forcing Re[]'s to be Real

*To*: mathgroup at smc.vnet.net*Subject*: [mg18234] Re: [mg18223] Forcing Re[]'s to be Real*From*: Haiduke Sarafian <has2 at psu.edu>*Date*: Thu, 24 Jun 1999 14:24:17 -0400*Sender*: owner-wri-mathgroup at wolfram.com

At 08:41 PM 6/22/99 -0400, Anthony Foglia wrote: > I seem to have found an interesting problem involving computing the >real part of complex numbers. (Interesting, in that it wasn't there a few >weeks ago when I ran the (as-far-as-i-can-remember) exact same code.) > >I have a complex function: > >k[w] := Sqrt[w^2 (1 + (2 / (1 + I w)))] > >I want to graph the real and imaginary parts, but Mathematica doesn't want >to express the Re[k[w]] as a real number. What do I mean? Well, if I >type: > >Re[Sqrt[1+I]] > >I get out > >Re[Sqrt[1+I]] > >Same if I do Re[ComplexExpand[Sqrt[1+I]]], or Re[(1+I)^(1/2)]. But if I >enter: > >Re[ComplexExpand[(1+I)^(1/2)] > >Mathematica is kind enough to respond with: > >2^(1/4) Cos[Pi/8] > >I'm certain that this is the root of my problem, but I'll be damned if I >know why Mathematica doesn't like it now, but did a few weeks ago. Any >help? > >--Anthony > Anthony; the source of the problem is the argument of k[w] function - It should read k[w_]:=... As you suggested, to extract the Re and Im components of k[w] apply Re[ComplexExpand[k[w]] and Im[ComplexExpand[k[w]] - then you can graph the outputs. Cheers