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Re: Re: with 5.2 Mac

  • To: mathgroup at smc.vnet.net
  • Subject: [mg59804] Re: [mg59783] Re: with 5.2 Mac
  • From: Pratik Desai <pdesai1 at umbc.edu>
  • Date: Mon, 22 Aug 2005 02:48:21 -0400 (EDT)
  • References: <de6lnl$cfa$1@smc.vnet.net> <200508210751.DAA26532@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Steuard Jensen wrote:

>[Reversed order of quotes to make the discussion easier to read:]
>
>  
>
>>From: Steuard Jensen [mailto:sbjensen at midway.uchicago.edu]
To: mathgroup at smc.vnet.net
>>    
>>
>>>I've just upgraded from Mathematica 5.0 to 5.2 for the Mac...
>>>      
>>>
>
>  
>
>>>Specifically, I have used $Assumptions to define some variables as
>>>real.  I apply Conjugate to various expressions, and then Simplify
>>>the results.  In version 5.0, I _never_ saw a case in which
>>>Conjugate[] remained after this step.  But in 5.2, I find that
>>>even simple forms like Conjugate[x + I y] often remain
>>>unsimplified.  (Refine[x + I y] still seems to work, though.)
>>>      
>>>
>
>Quoth "David Park" <djmp at earthlink.net> in article
><de6lnl$cfa$1 at smc.vnet.net>:
>  
>
>>Why don't you use...
>>
>>ComplexExpand[Conjugate[x + I y]]
>>x - I*y
>>
>>and you don't even have to set $Assumptions?
>>    
>>
>
>That would be an excellent suggestion for this case, but my actual
>work isn't this simple.  In particular, my actual expressions include
>a mix of complex-valued and real-valued terms.  So either I would have
>to use $Assumptions as I've done here, or I would have to pass a long
>list of complex variables to ComplexExpand each time.  (And it's even
>possible that my extra TransformationFunctions might replace
>combinations of complex variables with real ones, so I might have to
>use ComplexExpand more than once.)
>
>In any case, whether or not ComplexExpand is the _best_ way to do
>this, I think that Simplify still ought to work as expected! :)
>
>Nevertheless, thanks for your suggestion; even if it's not right for
>this problem, it could be useful for others.
>
>						Steuard Jensen
>
>  
>
Here is a somewhat inelegant yet effective approach, instead of using 
Assumption
Use TagSet to define your really "real" variables

Clear[a, b, z]
TagSet[a, Conjugate[a], a]
TagSet[b, Conjugate[b], b]
z = a + I*b // Conjugate
I use this solution as a last recourse...but it works every time


Best Regards

Pratik



-- 
Pratik Desai
Graduate Student
UMBC
Department of Mechanical Engineering
Phone: 410 455 8134



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