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Re: force variable to be real

  • To: mathgroup at smc.vnet.net
  • Subject: [mg91777] Re: [mg91736] force variable to be real
  • From: "peter lindsay" <pl.0 at me.com>
  • Date: Sun, 7 Sep 2008 22:53:03 -0400 (EDT)
  • References: <200809070933.FAA25407@smc.vnet.net>

Paul,
you seem to be using := but anyway, I hope below helps,
Peter

In[39]:= w=x+I 2 x z
Out[39]= x+2 I x z
In[40]:= real=ComplexExpand[Re[w]]
Out[40]= x
In[41]:= imag=ComplexExpand[Im[w]]
Out[41]= 2 x z
In[42]:= D[real,x]
Out[42]= 1

2008/9/7 phillman5 <PHILLMAN5 at gmail.com>:
> 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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