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MathGroup Archive 2005

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Re: Re: Re: symbolic complex expressions

  • To: mathgroup at smc.vnet.net
  • Subject: [mg53781] Re: [mg53759] Re: Re: [mg53637] symbolic complex expressions
  • From: Pratik Desai <pdesai1 at umbc.edu>
  • Date: Thu, 27 Jan 2005 05:41:19 -0500 (EST)
  • References: <200501260937.EAA00248@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Bob Hanlon wrote:

>$Version
>
>5.1 for Mac OS X (October 25, 2004)
>
>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)
>
>There is no indication that ComplexExpand has changed from v4.2 to v5.1
>
>Try starting with a fresh kernel.
>
>
>Bob Hanlon
>
>  
>
>>From: "Frank Deicke" <frankdeicke at gmx.de>
To: mathgroup at smc.vnet.net
>>    
>>Date: 2005/01/25 Tue AM 10:44:48 EST
>>CC: mathgroup at smc.vnet.net
>>Subject: [mg53781] [mg53759] Re: [mg53637] symbolic complex expressions
>>
>>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
>>>>Subject: [mg53781] [mg53759] [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
>>>>
>>>>
>>>>        
>>>>
>>-- 
>>GMX im TV ... Die Gedanken sind frei ... Schon gesehen?
>>Jetzt Spot online ansehen: http://www.gmx.net/de/go/tv-spot
>>
>>    
>>
>
>  
>
Try this for the first part

Clear[a,b]
TagSet[a,Im[a],0]
TagSet[b,Im[b],0]
TagSet[a,Re[a],a]
TagSet[b,Re[b],b]
lamda=a+I*b
ComplexExpand[Abs[lamda]]

 >>


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