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MathGroup Archive 2001

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complex coefficients and rules...

  • To: mathgroup at smc.vnet.net
  • Subject: [mg28203] complex coefficients and rules...
  • From: Richard Easther <easther at physics.columbia.edu>
  • Date: Wed, 4 Apr 2001 04:13:25 -0400 (EDT)
  • Organization: Inst. for Strings, Cosmology and Astroparticle Physics (ISCAP)
  • Sender: owner-wri-mathgroup at wolfram.com

Hi, 

I am having some trouble applying some simple rules to complex
expressions. 

For instance,

 Exp[-4 I y] /. I-> -I

yields

 Exp[-4 I y]

This seemed a bit odd, so I looked at the "full form" and found,

Power[E, Times[Complex[0, -4], y]]

However, trying the match 

 Exp[-4 I y] /. a_ I -> -a I

doesn't work either, since FullForm[a I ]  is Times[Complex[0, -1], a]
and so the patterns do not match.  

All I want is a simple complex conjugate (the Conjugate function does
not assume that y is real), that maps I->-I. The more tricky 

 Exp[-4 I y] /. Complex[a_ ,b_] -> Complex[a,-b] 

does work, but it is seems a little cumbersome.

In any case my question is: is there a general way to avoid having to do
this, or is Mathematica always going to assume that any algebraic
constant is potentially complex?

Richard


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