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Re: Bug in Mathematica 7.0.1.0 ?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg109356] Re: Bug in Mathematica 7.0.1.0 ?
  • From: David Bailey <dave at removedbailey.co.uk>
  • Date: Fri, 23 Apr 2010 03:48:29 -0400 (EDT)
  • References: <hqmd2g$pro$1@smc.vnet.net> <hqmoku$4d7$1@smc.vnet.net> <hqott8$9c5$1@smc.vnet.net>

slawek wrote:
> U=BFytkownik "David Bailey" <dave at removedbailey.co.uk> napisa=B3 w wiadomo=B6ci
> grup dyskusyjnych:hqmoku$4d7$1 at smc.vnet.net...
>> 1)  The answer from 7.0.1 is not wrong - just not in the form you desired.
> 
> Thanks for a reply.
> 
> It is wrong because Mathematica should present results in the simplest form
> and the Conjugate[a] is not the simplest form.
> 
>> 2)  Your code assumed that Conjugate called Im internally - this is the
>> sort of assumption that may vary from one version to the next.
> 
> Mathematica should check all data on a symbol: is it real? is it complex? is
> it a matrix? is it a constant? The Im[variable]^=0 was a well known practice
> to define that a variable is real. Nevertheless you are right: Mathematica
> degrade from older to 6.0 and 7.0 versions - no more RealsOnly, no ReIm, no
> working Conjugate. Some changes was forced by poor implementation - e.g.
> RealsOnly gives horrible wrong results in some cases.
> 
>> FullSimplify[Conjugate[a b], Im[a] == 0]
> 
> %/.Conjugate[a b]->a Conjugate[b] is far more simple anyway.
> 
>> Conjugate[b]) is actually no simpler than Conjugate[a b]
> 
> Your point of view. I have some nasty integrals, and Conjugate[a b] glue to
> a^4 to give a^5 Integrate[Conjugate[b]...., ...]. I think that a^5 as a
> factor is a little simpler than Conjugate[a b] inside Integrate.
> 
Try comparing:

a Conjugate[b] // TreeForm

and

Conjugate[a b] //TreeForm

If you do this, you will see why I said that neither was more simple 
than the other. This often happens - one form may be more desirable than 
another for some purpose without being simpler.

David Bailey
http://www.dbaileyconsultancy.co.uk


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