Re: force variable to be real

*To*: mathgroup at smc.vnet.net*Subject*: [mg91778] Re: force variable to be real*From*: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>*Date*: Sun, 7 Sep 2008 22:53:14 -0400 (EDT)*References*: <ga0744$opl$1@smc.vnet.net>

phillman5 wrote: > 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. You could use *ComplexExpand[]*, which assumes that all the variables -- x and y in your example -- are real, in the definition of y. In[1]:= w := x + I 2 x z y := ComplexExpand[Re[w]] D[y, x] Out[3]= 1 Regards, -- Jean-Marc