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MathGroup Archive 1999

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Re: Finding real part (newbie question)

  • To: mathgroup at smc.vnet.net
  • Subject: [mg15767] Re: Finding real part (newbie question)
  • From: Count Dracula <lk3a at sparc20-3.unixlab.virginia.edu>
  • Date: Sun, 7 Feb 1999 02:03:49 -0500 (EST)
  • Organization: University of Virginia
  • Sender: owner-wri-mathgroup at wolfram.com

Gnalle <GNALLE at MMF.ruc.dk> writes:

> If a,b,c,d are real numbers. How do I use mathematica to find the real
> part of

> 1/(a + I b + 1/(c + I d))

Try using ComplexExpand or use the standard package Algebra`ReIm.m. With
the definition

RealPart[expr_] := 
 (Cases[expr, z_Symbol :> (z /: Im[z] = 0) , Infinity];
Simplify[Re[expr]])


and expr = 1/(a + I b + 1/(c + I d)), RealPart[expr] gives

                               2      2
                        c + a c  + a d
        -----------------------------------------------
                             2   2    2     2   2    2
        1 + 2 a c - 2 b d + a  (c  + d ) + b  (c  + d )
-- 
_________________________________________________________________________
Levent Kitis                            
lk3a at esmeralda.mech.virginia.edu University of Virginia Department of
Mechanical and Aerospace Engineering
_________________________________________________________________________


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