Re: Replace

*To*: mathgroup at yoda.physics.unc.edu*Subject*: Re: Replace*From*: p617hfa at sun24.mpifr-bonn.mpg.de (Heino Falcke)*Date*: Fri, 9 Oct 92 09:36:51 +0100

John Pender complains: >In[4]:= 5 I /. I->-I > >Out[4]= 5 I ************* what the hell? > >the fact that mma won't make the substitution if there is anything in front >of I in the expression of interest blows the whole deal. Just have a look at complex numbers with FullForm. Don't get confused by the OutputForm I representation. In[1]:= FullForm[5 I] Out[1]//FullForm= Complex[0, 5] In[2]:= FullForm[-I] Out[2]//FullForm= Complex[0, -1] The correct substitution would be Complex[a_,b_] :> Complex[a,-b] But it's true this is a little bit confusing. Heino Falcke