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Re: Finding real part (newbie question)
*To*: mathgroup at smc.vnet.net
*Subject*: [mg15760] Re: [mg15722] Finding real part (newbie question)
*From*: "Kevin J. McCann" <kevinmccann at home.com>
*Date*: Sun, 7 Feb 1999 02:03:44 -0500 (EST)
*Sender*: owner-wri-mathgroup at wolfram.com
There is more than one way to do this. The one which I use follows. It
is not pretty.
The problem is how to tell Mathematica that a,b,c,d are real. I assume
this is what you
meant.
(* Load the package *)
<<Algebra`ReIm`
(* The following "^=" are called Upsets and they *) (* tell the
operations Re,Im what to do when the symbols are encountered *)
Re[a]^=a;Im[a]^=0;
Re[b]^=b;Im[b]^=0;
Re[c]^=c;Im[c]^=0;
Re[d]^=d;Im[d]^=0;
(* Now for your problem *)
exp=1/(a + I b + 1/(c + I d))
Re[exp]//Simplify
(* to get a better feeling about this, try the following two *)
Re[a+I b]
a
Re[x + I y]
-Im[y]+Re[x]
The difference is that Mathematica doesn't know that x and y are real -
and maybe they aren't.
Kevin
-----Original Message-----
From: Gnalle <GNALLE at MMF.ruc.dk>
To: mathgroup at smc.vnet.net
Subject: [mg15760] [mg15722] Finding real part (newbie question)
>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))
>
>Yes I can calculate it by hand, but I would like to know how to use
>Mathematica.
>--
>
> Niels Langager Ellegaard
> 'http://mmf.ruc.dk/~gnalle/'
>
>
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