Re: Bug in Mathematica 220.127.116.11 ?
- To: mathgroup at smc.vnet.net
- Subject: [mg109356] Re: Bug in Mathematica 18.104.22.168 ?
- From: David Bailey <dave at removedbailey.co.uk>
- Date: Fri, 23 Apr 2010 03:48:29 -0400 (EDT)
- References: <firstname.lastname@example.org> <email@example.com> <firstname.lastname@example.org>
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