Re: Symbolic complex conjugation?

*To*: mathgroup at smc.vnet.net*Subject*: [mg89974] Re: Symbolic complex conjugation?*From*: magma <maderri2 at gmail.com>*Date*: Wed, 25 Jun 2008 06:30:01 -0400 (EDT)*References*: <g3q7vb$aus$1@smc.vnet.net>

On Jun 24, 9:32 am, AES <sieg... at stanford.edu> wrote: > I'm sorry, but I just don't understand why the following test case works > just fine: > > [In copying it, I've substituted "Isymbol" for the \[ImaginaryI] that > actually appears in the Out[] cells.] > > In[202]:= eqna={a+I b==0}; > solna=Solve[eqna,b]; > b=b/.solna[[1]]; > bStar=b/.{I->-I}; > {b, Star} > > Out[205]={ -Isymbol a, Isymbol a } > > but the actual calculation that prompted the test case doesn't: > > In[206]:= eqnp={((dwa/2)+I(w-wa))p-I (kappa/(2 w))dN e==0}; > solnp=Solve[eqnp,p]; > p=p/.solnp[[1]]; > pStar=p/.{I->-I} > > Out[208]= { (dN e kappa)/(w (-Isymbol dwa+2 w-2 wa)), > (dN e kappa)/(w (-Isymbol dwa+2 w-2 wa)) } > > And actually, I guess my real concern is not understanding "how it > happens" -- but more "how it can happen" that Mathematica can do > something this potentially damaging to some innocent user. Changing I into -I is not a good idea. Never. In your p you have -I which is internally Complex[0,-1] as you can see with p//FullForm So your I->-I is never carried out. In your test case b was I a , so the replacement was carried out. If you want to Conjugate a complex number p, use Conjugate[p] and then ComplexExpand, if all your variables are supposed to be Real. ComplexExpand[Conjugate[p]] will give you the correct answer.