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