Subject: double integrals seem to give different answers
From: Richard Hennessy
Date: Sat, 21 Nov 2009 19:36:53 -0500
I think (w^2)^(3/2) should simplify to abs(w^3) or abs(w)^3 when the domain
system variable is set to "real". Maybe I should add this to pw.mac, since
it's true if you stick to the assumption that all variables are real (which
is what domain I think should mean). Since domain does not work maybe I can
add a new feature to pw, which always assumes only real numbers. I haven't
checked to see if pw can can do this case.
Rich
--------------------------------------------------
From: "Richard Fateman" <fateman at cs.berkeley.edu>
Sent: Saturday, November 21, 2009 7:14 PM
To: "Maxima List" <maxima at math.utexas.edu>
Cc: "G. Jay Kerns" <gkerns at ysu.edu>
Subject: Re: [Maxima] double integrals seem to give different answers
> Richard Hennessy wrote:
>> This is a bug,
> ...
> If you think that (w^2)^(3/2) should simplify to abs(w^3), then you
> inevitably run into problems.
> That is what trigsimp, or some component of it, believes.
> If you believe, as I do, that there are 2 values, +w^3 and -w^3, and the
> computation should proceed
> using Both values until
> (a) it is determined that It Doesn't Matter Which You Use.
> or
> (b) the user (or some other computation) decides that Only One Value
> Works and uses it.
> or
> (c) you have to produce an answer Including Both Values.
>
> From this perspective it isn't a bug in integration or trigsimp. And I
> suspect the same trick will catch you in
> Mathematica or Maple, if they do the same "simplification". There are a
> large number of system-independent
> mathematical "gotchas".
>
> RJF
>
>
>
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