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MathGroup Archive 2000

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Re: global real variables

  • To: mathgroup at smc.vnet.net
  • Subject: [mg22098] Re: global real variables
  • From: "Allan Hayes" <hay at haystack.demon.co.uk>
  • Date: Mon, 14 Feb 2000 02:03:50 -0500 (EST)
  • References: <87trds$5o3@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Naum.
I'll take the last part of your question first.

Here is a way to reduce the labour of saying what is real:

Simplify[#1, Element[Join[#2, #2^-1], Reals] ] &[#, Level[#, {-1}]] &[
  Conjugate[ x + x * p^-1 ]]

(1 + 1/p)*x

But then, for your question about global real variables I went back to the
AddOn:

<< Algebra`ReIm`

Surprisingly, this helps  Simplify:

Simplify[ Conjugate[ x + x * p^-1 ] , Element[ {x, p} , Reals ] ]

(1 + 1/p)*x

But, to come back to the global real variables, we enter

x /: Im[x] = 0;
p /: Im[p] = 0;

and then find:

Conjugate[ x + x * p^-1 ]

x + x/p

Allan
---------------------
Allan Hayes
Mathematica Training and Consulting
Leicester UK
www.haystack.demon.co.uk
hay at haystack.demon.co.uk
Voice: +44 (0)116 271 4198
Fax: +44 (0)870 164 0565



"Naum Phleger" <naum at cava.physics.ucsb.edu> wrote in message
news:87trds$5o3 at smc.vnet.net...
>     I asked a dumb question a few weeks ago about making variables real
and
> found that Mathematica 4 took care of this better.  I have been using it
> since.  I still have a couple of problems with it though.  First, I can
have
> variables be treated as real by using the assumption Element[x,Reals] in a
> simplify command, but I want x to be real in all commands so I don't have
to
> keep using Simplify each time I want x to be recognized as real.  Second,
> even this doesn't seem to work quite right.  Here is what I mean.
>
>
>     Say I have tow var.s, x and p.  Both are real so I can do this.
>
> Simplify[ Conjugate[ x ] , Element[ x , Reals ] ]  ----> x
>
> amd I get the same thing for p, but it stops working if I have functions
of
> x and p, for instance I get
>
>
> Simplify[ Conjugate[ x + x * p^-1 ] , Element[ {x,p} , Reals ] ]  ---->
>
>  Conjugate[ x + x * p^-1 ]
>
>
> It works if I use FullSimplify   AND   put p^-1 into the list of variables
> that I want to have real.  How can I get around this without listing every
> negative power of every variable and wasting time with FullSimplify.
Thanks
> for any help.  Thanks.
>
>
>                 -NAUM
>



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