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