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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
>
>
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