MathGroup Archive 2013

[Date Index] [Thread Index] [Author Index]

Search the Archive

Re: How to get the Real and Imaginary part of an expression

  • To: mathgroup at smc.vnet.net
  • Subject: [mg129328] Re: How to get the Real and Imaginary part of an expression
  • From: "Nasser M. Abbasi" <nma at 12000.org>
  • Date: Sat, 5 Jan 2013 02:17:05 -0500 (EST)
  • Delivered-to: l-mathgroup@mail-archive0.wolfram.com
  • Delivered-to: l-mathgroup@wolfram.com
  • Delivered-to: mathgroup-newout@smc.vnet.net
  • Delivered-to: mathgroup-newsend@smc.vnet.net
  • References: <kc2pi7$mdh$1@smc.vnet.net>
  • Reply-to: nma at 12000.org

On 1/2/2013 8:14 PM, Eduardo M. A. M. Mendes wrote:
> Hello
>
> I need to extract the real and imaginary part of the following expression
>
> (w=882)/(s^2+2*z*w*s+w^2)
>
> where w and z are positive constants.  s is a complex variable.
>
> Applying Re and Im to the expression does not do much.   By hand, one can easily find them.
>

You can use ComplexExpand.

For example

----------------
expr = s + 2 I b + c
ComplexExpand[Re[expr]]
   (* c + s *)

ComplexExpand[Im[expr]]
   (* 2 b *)
-------------------

For your example, I might do

Clear[s, z, w, a, b];
expr = w/(s^2 + 2*z*w*s + w^2);
ComplexExpand[Re[expr /. s -> a + I b]]

--Nasser



  • Prev by Date: Re: How to get the Real and Imaginary part of an expression
  • Next by Date: Re: Phantom Error Messages in v9
  • Previous by thread: Re: How to get the Real and Imaginary part of an expression
  • Next by thread: get all Section cells