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MathGroup Archive 2005

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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


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