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MathGroup Archive 2000

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global real variables

  • To: mathgroup at smc.vnet.net
  • Subject: [mg22019] global real variables
  • From: Naum Phleger <naum at cava.physics.ucsb.edu>
  • Date: Thu, 10 Feb 2000 02:26:07 -0500 (EST)
  • Sender: owner-wri-mathgroup at wolfram.com

    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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