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MathGroup Archive 2001

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Re: complex coefficients and rules...

  • To: mathgroup at smc.vnet.net
  • Subject: [mg28211] Re: complex coefficients and rules...
  • From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
  • Date: Thu, 5 Apr 2001 03:00:26 -0400 (EDT)
  • Organization: Universitaet Leipzig
  • References: <9aelr6$nbu@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Hi,

the online help (Conjugate|Further Examples) say:

Exp[-4 I y] /. Complex[0, a_] :> Complex[0, -a]

And it *is* the "official" way, even if you don't like it.
The reason is that Complex[1,2] is a numerical data type
and 

a+I*b 

with symbolic a and b is *not* Complex[a,b] it is

Plus[a,Times[Complex[0,1],b]]


Regards
  Jens

Richard Easther wrote:
> 
> 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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