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

*To*: mathgroup at smc.vnet.net*Subject*: [mg129327] Re: How to get the Real and Imaginary part of an expression*From*: Bob Hanlon <hanlonr357 at gmail.com>*Date*: Sat, 5 Jan 2013 02:16:45 -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*: <20130103021627.CBD1368B0@smc.vnet.net>

expr = (w = 882)/(s^2 + 2*z*w*s + w^2); re = Re[ComplexExpand[expr, s]] // Simplify[#, Element[z, Reals]] &; im = Im[ComplexExpand[expr, s]] // Simplify[#, Element[z, Reals]] &; expr == re + I*im // FullSimplify True Using a concrete example s2 = RandomComplex[] // Rationalize[#, 0] &; re2 = re /. s -> s2 // Simplify[#, Element[z, Reals]] &; im2 = im /. s -> s2 // Simplify[#, Element[z, Reals]] &; (expr /. s -> s2) == re2 + I*im2 // Simplify True Bob Hanlon On Wed, Jan 2, 2013 at 9:16 PM, Eduardo M. A. M. Mendes <emammendes at gmail.com> 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. > > What am I missing? > > many thanks > > Ed > > >

**References**:**How to get the Real and Imaginary part of an expression***From:*"Eduardo M. A. M. Mendes" <emammendes@gmail.com>