Re: Re: Extracting Re and Im parts of a symbolic expression
- To: mathgroup at smc.vnet.net
- Subject: [mg42093] Re: [mg42077] Re: Extracting Re and Im parts of a symbolic expression
- From: Andrzej Kozlowski <akoz at mimuw.edu.pl>
- Date: Thu, 19 Jun 2003 03:58:55 -0400 (EDT)
- Sender: owner-wri-mathgroup at wolfram.com
All that this amounts really is that ComplexExpand may not be the most fortunate name for this particular function. If instead it was called EvaluateAssumingThatAllVariablesAreRealExceptTheSpecifiedOnes, would it make it clearer? Andrzej Kozlowski Yokohama, Japan http://www.mimuw.edu.pl/~akoz/ http://platon.c.u-tokyo.ac.jp/andrzej/ On Wednesday, June 18, 2003, at 03:10 PM, AES/newspost wrote: > In article <bcmodv$sm8$1 at smc.vnet.net>, > Andrzej Kozlowski <akoz at mimuw.edu.pl> wrote: > >> Note that CompelxExpand[Re[z]] works, Re[ComplexExpand[z]] is >> pointless >> since it is just Re[z]. > > And the reason why this question keeps coming up year after year on > this > newsgroup (and why I have to look up the answer in my own online > "Mathematica > Notes" notebook almost every time I use this construct) is that the > intuitive way any normal user would write an expression to get the real > part of an expression is > > Re[ComplexExpand[expr]] > > whereas the "correct" Mathematica statement > > ComplexExpand[Re[expr]] > > is under any normal interpretation an absurd way of expressing what the > user wants. > > [In real life compound expressions almost expand **from the inside > out**: If you want the log of the sin of z you write Log[Sin[z]]. > So, > the second expression above says you're going to take the REAL part of > expr, and then COMPLEX-EXPAND the result, even though the result is > something that's already explicitly real, right? > > Don't both explaining again **why** it works this way -- my only point > is that maybe in a larger picture of the logical design of Mathematica > syntax it has to be structured this way, but unfortunately it's an > intrinsically confusing way of expressing the user's objective, and > always will be.] > > -- > "Power tends to corrupt. Absolute power corrupts absolutely." > Lord Acton (1834-1902) > "Dependence on advertising tends to corrupt. Total dependence on > advertising corrupts totally." (today's equivalent) > > >