Re: symbolic complex expressions

*To*: mathgroup at smc.vnet.net*Subject*: [mg53671] Re: symbolic complex expressions*From*: highegg at centrum.cz (highegg)*Date*: Sat, 22 Jan 2005 03:51:56 -0500 (EST)*References*: <kz2idri63hl7@legacy>*Sender*: owner-wri-mathgroup at wolfram.com

Hi, the answer is simple - Mathematica assumes that all variables are _complex_ by default. In order to obtain the desired simplifications, you first have to tell Mathematica that x, y are real. The ComplexExpand[] function is well suited for this, see the help another way is to use Simplify with Assumptions->{x \[Element] Reals} etc. Regards, highegg On 20 Jan 05 10:03:32 -0500 (EST), Frank wrote: >Hi, > >I've 2 question with mathematica using symbolic complex expressions. > >- Is there a possibility to make from i.e. |x + I y| -> sprt(x^2+y^2) >if x and y are Real. Abs[] doesn't work? > > >- You've a fraction like this x/(x + I y) and you want to eliminate >the complex expression in the denominator. >i.e. doing something like this: x/(x + Iy)*(x - I y)/(x - I y) -> (x^2 >- I x y)/(x^2+y^2) > >How do you do this with mathematica? > >Thanks, > >Frank