[Maxima-bugs] [ maxima-Bugs-1372477 ] log(neg integer) not fully simplified/fix

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Bugs item #1372477, was opened at 2005-12-03 14:09
Message generated for change (Comment added) made by willisbl
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Category: Lisp Core - Simplification
Group: Includes proposed fix
>Status: Closed
>Resolution: Fixed
Priority: 5
Private: No
Submitted By: Barton Willis (willisbl)
Assigned to: Nobody/Anonymous (nobody)
Summary: log(neg integer) not fully simplified/fix

Initial Comment:
(%i1) declare(n,integer);
(%o1) DONE
(%i2) assume(n > 0);
(%o2) [n>0]
(%i3) log(-n^2), lognegint, logexpand;

An extra log expand is needed:

(%o3) log(n^2)+%i*%pi
(%i4) %,logexpand;
(%o4) 2*log(n)+%i*%pi

A putative fix; in simpln, replace

(add2 '((mtimes simp) $%i $%pi)
  (cond ((equal y -1) 0) (t (list '(%log simp) (neg y))))))

with something like

(and $lognegint (maxima-integerp y) (eq ($sign y) '$neg))
 (add (mul '$%i '$%pi) (take '(%log) (neg y))))

If both ($sign y) and ($sign (neg y)) evaluate
to '$neg, we're toast.  But that would never
happen...

Barton



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>Comment By: Barton Willis (willisbl)
Date: 2008-03-09 07:45

Message:
Logged In: YES 
user_id=895922
Originator: YES

Fixed by simp.lisp cvs revision 1.53.

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Comment By: Robert Dodier (robert_dodier)
Date: 2006-08-14 21:43

Message:
Logged In: YES 
user_id=501686

Observed in 5.9.3cvs.

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