From bug-octave-request at che dot utexas dot edu  Mon Sep 12 11:04:25 1994
Subject: Operator not working as documented
From: Edward Scott Meadows <esm at che dot utexas dot edu>
To: bug-octave
Date: Mon, 12 Sep 1994 11:04:05 -0500


>From "help -i \"

`X \ Y'
Left division.  This is conceptually equivalent to the expression

inverse (x) * y

but it is computed without forming the inverse of `x'.

If the system is not square, or if the coefficient matrix is
singular, a minimum norm solution is computed.

Here's octave result:

octave:92> as
as =

0.4439261   0.2667981  -0.2851065   0.1788201   0.1680353
0.0595516   0.1134210  -0.0888729   0.1309631  -0.0561448
0.4253507  -0.1039117   0.1132885  -0.4033794   0.6157430
-0.4067916   0.0235994   0.0071662   0.2468884  -0.4727989
0.7199150   0.1704362  -0.2010408  -0.1184546   0.5919530

octave:93> eig(as)
ans =

0.73861 + 0.59504i
0.73861 - 0.59504i
0.03225 + 0.00000i
0.00000 + 0.00000i
-0.00000 + 0.00000i

octave:94> vs
vs =

-1.00148
-1.10857
-0.50165
-1.37176
-0.63761

octave:95> as\vs
error: matrix singular to machine precision, rcond = 8.9811e-18
error: evaluating binary operator `\' near line 95, column 3

What happened to minimum norm solution?  I knew in advance that as was
singular.  I needed the promised minimum norm solution to proceed.

--esm