It seems to work for me:
(%i10) Minvinv:invert_by_lu(invert_by_lu(M));
(%o10) matrix([1,0,0],[v[[1,0],[0,0]],1,0],[v[[0,1],[0,0]],v[[0,1],[1,0]],1])
(%i11) build_info();
Maxima version: 5.25.0
Maxima build date: 16:14 8/15/2011
Host type: i686-pc-mingw32
Lisp implementation type: GNU Common Lisp (GCL)
Lisp implementation version: GCL 2.6.8
(%o11)
--Barton
-----maxima-bounces at math.utexas.edu wrote: -----
To: maxima at math.utexas.edu
From: andre maute
Sent by: maxima-bounces at math.utexas.edu
Date: 01/08/2012 06:00PM
Subject: invert_by_lu does not work as expected
Hi list,
I have the following maxima file with output,
where a double invocation of invert_by_lu results in an error
Regards
Andre
----------- matrix_bug.max ----------------
display2d : false;
M : matrix([1,0,0],[v[[1,0],[0,0]],1,0],[v[[0,1],[0,0]],v[[0,1],[1,0]],1]);
/* works */
Minv : invert(M);
Minvinv : invert(invert(M));
/* doesn't work */
Minv : invert_by_lu(M);
Minvinv : invert_by_lu(invert_by_lu(M));
----------- matrix_bug.max ----------------
----------- matrix_bug.txt ----------------
Maxima 5.24.0 http://maxima.sourceforge.net
using Lisp SBCL 1.0.40-1.fc14
Distributed under the GNU Public License. See the file COPYING.
Dedicated to the memory of William Schelter.
The function bug_report() provides bug reporting information.
(%i1) ? ? ? ? ? ? ? ? ? ? ? ?batch(matrix_bug.max)
read and interpret file: /home/user/matrix_bug.max
(%i2) ? ? ? ? ? ? ? ? ? ? ? ? ?display2d : false
(%o2) false
(%i3)
M:matrix([1,0,0],[v[[1,0],[0,0]],1,0],[v[[0,1],[0,0]],v[[0,1],[1,0]],1])
(%o3) matrix([1,0,0],[v[[1,0],[0,0]],1,0],[v[[0,1],[0,0]],v[[0,1],[1,0]],1])
(%i4) Minv:invert(M)
(%o4) matrix([1,0,0],[-v[[1,0],[0,0]],1,0],
?? ? ? ? ? ? ?
[v[[0,1],[1,0]]*v[[1,0],[0,0]]-v[[0,1],[0,0]],-v[[0,1],[1,0]],1])
(%i5) Minvinv:invert(invert(M))
(%o5) matrix([1,0,0],[v[[1,0],[0,0]],1,0],[v[[0,1],[0,0]],v[[0,1],[1,0]],1])
(%i6) Minv:invert_by_lu(M)
(%o6) matrix([1,0,0],[-v[[1,0],[0,0]],1,0],
?? ? ? ? ? ? ?
[v[[0,1],[1,0]]*v[[1,0],[0,0]]-v[[0,1],[0,0]],-v[[0,1],[1,0]],1])
(%i7) Minvinv:invert_by_lu(invert_by_lu(M))
Maxima encountered a Lisp error:
??The value NIL is not of type CHARACTER.
Automatically continuing.
To enable the Lisp debugger set *debugger-hook* to nil.
(%o8) "/home/user/matrix_bug.max"
----------- matrix_bug.txt ----------------
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[attachment "matrix_bug.max" removed by Barton Willis/MATH/UNK/UNEBR]
[attachment "matrix_bug.txt" removed by Barton Willis/MATH/UNK/UNEBR]