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MathGroup Archive 2005

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Re: symbolic complex expressions

  • To: mathgroup at smc.vnet.net
  • Subject: [mg53674] Re: [mg53637] symbolic complex expressions
  • From: "David Park" <djmp at earthlink.net>
  • Date: Sat, 22 Jan 2005 03:52:03 -0500 (EST)
  • Sender: owner-wri-mathgroup at wolfram.com

Frank,

When working with complex expressions YOU WILL ALMOST ALWAYS WANT TO USE
ComplexExpand. ComplexExpand is the workhorse of complex algebra. (They
should have called it ComplexSimplify.) You will often want to use the
TargetFunctions option with it. Certainly read the Help for ComplexExpand
and experiment with it.

Abs[x + I y]
% // ComplexExpand
Abs[x + I*y]
Sqrt[x^2 + y^2]

David Park
djmp at earthlink.net
http://home.earthlink.net/~djmp/

From: Frank [mailto:frankdeicke at gmx.de]
To: mathgroup at smc.vnet.net

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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