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MathGroup Archive 2005

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Re: Re: symbolic complex expressions

  • To: mathgroup at smc.vnet.net
  • Subject: [mg53774] Re: [mg53746] Re: [mg53637] symbolic complex expressions
  • From: "David Park" <djmp at earthlink.net>
  • Date: Thu, 27 Jan 2005 05:41:09 -0500 (EST)
  • Sender: owner-wri-mathgroup at wolfram.com

Frank,

Version 5 ComplexExpand seems to work better than Version 4.2.  In 4.2 you
have to use...

ComplexExpand[Abs[x + I*y], TargetFunctions -> {Re, Im}]
Sqrt[x^2 + y^2]

ComplexExpand[x/(x + I*y), TargetFunctions -> {Re, Im}]
x^2/(x^2 + y^2) - (I*x*y)/(x^2 + y^2)

In Version 5 you can leave out the TargetFunctions option.

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


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

Hi Bob,

I try this but it does not realy work fine. I use mathematica version 4.2.
Is there anything else like including a special package?

In: ComplexExpand[Abs[x + I*y]]
Out: Abs[x + I y] ???

or

In: ComplexExpand[x/(x+I*y)]
Out: x^2/Abs[x + I y]^2 - I x y/Abs[x + I y]^2 ???

Why you get another output?

Thanks,

Frank

> ComplexExpand[Abs[x+I*y]]
>
> Sqrt[x^2 + y^2]
>
> ComplexExpand[x/(x+I*y)]
>
> x^2/(x^2 + y^2) - (I*x*y)/(x^2 + y^2)
>
>
> Bob Hanlon
>
> >
> > From: frankdeicke at gmx.de (Frank)
To: mathgroup at smc.vnet.net
> > Date: 2005/01/21 Fri AM 06:35:44 EST
> > To: mathgroup at smc.vnet.net
> > Subject: [mg53774] [mg53746] [mg53637] symbolic complex expressions
> >
> > 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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