[Maxima-bugs] [ maxima-Bugs-838301 ] vect negate cross product simplification

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Bugs item #838301, was opened at 2003-11-08 03:17
Message generated for change (Comment added) made by crategus
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Category: Share Libraries
Group: None
>Status: Closed
>Resolution: Fixed
Priority: 5
Private: No
Submitted By: Stephen Leake (stephen_leake)
Assigned to: Nobody/Anonymous (nobody)
Summary: vect negate cross product simplification

Initial Comment:
load (vect);
declare (n, nonscalar)$
declare (r, nonscalar)$
declare (a, scalar)$
-a*r~n;

The current result is

     - a (- n) ~ r

In vect.mac, there is this declaration:

TELLSIMP(ETRUE~LESSP, -LESSP~ETRUE) $

If I change this to:

TELLSIMP(ETRUE~LESSP, -(LESSP~ETRUE)) $

the above expression reduces to:
    
    a n ~ r

which is better.


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>Comment By: Dieter Kaiser (crategus)
Date: 2010-05-09 23:32

Message:
The suggested fix has been committed in vect.mac revision 1.8.
Closing this bug report as fixed.
Dieter Kaiser

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Comment By: Dieter Kaiser (crategus)
Date: 2010-05-09 14:30

Message:
The current behavior of Maxima 5.20post is:

(%i1) load(vect)$
(%i2) declare([a,b],nonscalar)$
(%i3) declare(c,scalar)$

(%i4) c * a ~ b;
(%o4) c*a ~ b

This is the reported problem:

(%i5) c * b ~ a;
(%o5) c*(-a) ~ b

When we apply the suggested change we get in linear display:

(%i4) c * b ~ a;
(%o4) -c*a ~ b

In 2d-display the result looks like:

(%i6) c * b ~ a;
(%o6) - c (a ~ b)

There is a difference between linear and 2d-display only. The result is
   ((MTIMES SIMP) -1 $C (($~ SIMP) $A $B))

Dieter Kaiser

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You can respond by visiting: 
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