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/' > >