Re: force variable to be real

*To*: mathgroup at smc.vnet.net*Subject*: [mg91787] Re: force variable to be real*From*: "David Park" <djmpark at comcast.net>*Date*: Sun, 7 Sep 2008 22:54:52 -0400 (EDT)*References*: <ga0744$opl$1@smc.vnet.net>

When working with complex expressions one always wants to keep ComplexExpand handy. You will almost always have to use it. Re[x + I 2 x z] // ComplexExpand D[%, x] x 1 -- David Park djmpark at comcast.net http://home.comcast.net/~djmpark/ "phillman5" <PHILLMAN5 at gmail.com> wrote in message news:ga0744$opl$1 at smc.vnet.net... > How do you force variables to be real? > > I have > w:=x + I 2 x z, > and > y:=Re[w] > > and want the derivative of y wrt x, x and z are Real > D[y, x] > gives > Re'[x] - 2 z Im'[x z] > > where I'd expect just 1. Or I need to evaluate Re[w] forcing x and z > to be real, then take the derivative. > > Thank you for any help > Paul > >