Re: Is this a bug?

*To*: mathgroup at smc.vnet.net*Subject*: [mg90861] Re: Is this a bug?*From*: "David W.Cantrell" <DWCantrell at sigmaxi.net>*Date*: Sat, 26 Jul 2008 04:23:59 -0400 (EDT)*References*: <g6c982$brv$1@smc.vnet.net>

"mailcwc at gmail.com" <mailcwc at gmail.com> wrote: > I tried to solve the following equation with mathematica 6.03 > > Solve[{Abs[X+Y I]==5,X==3},{X,Y}] > > and got the answer > > {{X -> 3, Y -> -2 I}, {X -> 3, Y -> 8 I}} It's easy to verify that both of those solutions are correct. > Am I suppose to get {{X -> 3, Y -> 4 I}, {X -> 3, Y -> -4 I}} ? No. Rather, I think that you were wanting Y itself to be real, and so you should have been hoping for {{X -> 3, Y -> 4}, {X -> 3, Y -> -4}} instead. In any event, it seems that you were wanting Mathematica to find the possible imaginary parts of complex numbers having real part 3 and modulus 5. The way I'd do that is In[1]:= Reduce[Abs[3 + Im[z]*I] == 5, z] Out[1]= Im[z] == -4 || Im[z] == 4 Finally, in your title, you asked if there were a bug. Well, as I had said, the two solutions which your Solve gave are correct. But I think that Mathematica is perhaps at fault for not having warned you that Solve was not necessarily giving you all possible solutions. David