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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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