Fwd: Re: Maxima asks about sign of integration(!) variable



-------- Original Message --------
Subject: 	Re: [Maxima] Maxima asks about sign of integration(!) variable
Date: 	Wed, 25 Sep 2013 20:20:33 +0100
From: 	Jaime Villate <villate at fe.up.pt>
To: 	David Scherfgen <d.scherfgen at googlemail.com>, 
"maxima at math.utexas.edu" <maxima at math.utexas.edu>



Hi,
I agree, Maxima should not ask you about the sign of x in this case; to
get the correct result for that integral you actually have to separate
it into two parts:

(%i2) expr : sqrt(1+(4*x^(1/3)-1/16*x^((-1)/3))^2)$
(%i3) integrate(expr, x, -8, 0) + integrate(expr, x, 0, 512);
(%o3) 98739/8


Mathematica gives  3/16 (129 + 127 I Sqrt[3])
for the integral from -8 to 0.
Oddly, it takes it over 21 CPU seconds to come up with that.
for the integral from 0 to 512 it takes 0.53 seconds to give 12,294.



(no questions asked). The other problem (Maxima keeps asking the same
question again two more times) is a bug in versions 5.30.0 and 5.31.0.
The latest release (5.31.1) does not have that bug.

Regards,
Jaime

On 25-09-2013 09:08, David Scherfgen wrote:
> Hi,
>
> when I do:
>
> expr : sqrt(1+(4*x^(1/3)-1/16*x^((-1)/3))^2);
> integrate(expr, x, -8, 512);
>
> Maxima asks "Is x positive or negative?".
> Why does it ask that? x is the integration variable ... it shouldn't
> ask anything about it.
>
> Also, when I answer "positive;", Maxima keeps asking the same question
> again two more times.
> Only then, it gives me an answer.
>
> The whole asking thing seems very buggy to me ...
>
> David
> _______________________________________________
> Maxima mailing list
> Maxima at math.utexas.edu
> http://www.math.utexas.edu/mailman/listinfo/maxima

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