[Maxima-bugs] [ maxima-Bugs-1731624 ] asked about sign of yx in integral containing only z

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Bugs item #1731624, was opened at 2007-06-05 12:05
Message generated for change (Comment added) made by nobody
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Category: Lisp Core - Integration
Group: None
Status: Open
Resolution: None
Priority: 5
Private: No
Submitted By: Sanjoy Mahajan (sm324)
Assigned to: Nobody/Anonymous (nobody)
Summary: asked about sign of yx in integral containing only z

Initial Comment:
Entering
   integrate(exp(sqrt(z^3)),z,0,1);
produces

  Is  yx  positive or negative?

But there is no yx in the integrand.  I thought maxima might have an implicit rule about z = x + iy, so I tried the integral using q as the variable instead of z, but the same question was asked.

Maxima version: 5.12.0
Maxima build date: 3:18 5/23/2007
host type: i686-pc-linux-gnu
lisp-implementation-type: GNU Common Lisp (GCL)
lisp-implementation-version: GCL 2.6.7

(it's the Ubuntu 5.12.0-1ubuntu1 package from the upcoming release of Ubuntu recompiled on my Ubuntu feisty  system).

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Comment By: Nobody/Anonymous (nobody)
Date: 2007-12-12 07:43

Message:
Logged In: NO 

This is likely the same problem, but I am not completely sure, so I
decided to add this as a comment here rather than open a new bug report.

Entering:
limit(x*(1 - x*log(1 + 1/x)),x,0);
produces

Is  x + 1  positive or negative?

There are two things wrong with this

1) When x -> 0 then x+1 is clearly always positive. Presumably the
intended question was "Is x positive or negative?"
2) The value of the limit does not depend on the sign of x, it is 0 in
either case.

Maxima version: 5.13.99rc1
Maxima build date: 21:11 12/3/2007
host type: i686-redhat-linux-gnu
lisp-implementation-type: CLISP
lisp-implementation-version: 2.39 (2006-07-16) (built on
boulder.infotility.com [192.168.0.23])

(standard rpm from Sourceforge)

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Comment By: Robert Dodier (robert_dodier)
Date: 2007-07-17 13:10

Message:
Logged In: YES 
user_id=501686
Originator: NO

Another example (from the mailing list):

integrate( exp( sqrt(x) ), x, 1, 5);
 => Is  yx  positive or negative?

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You can respond by visiting: 
https://sourceforge.net/tracker/?func=detail&atid=104933&aid=1731624&group_id=4933