/usr/share/octave/packages/linear-algebra-2.2.0/@kronprod/not_done/eig.m is in octave-linear-algebra 2.2.0-1build1.
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##
## This program is free software; you can redistribute it and/or modify
## it under the terms of the GNU General Public License as published by
## the Free Software Foundation; either version 3, or (at your option)
## any later version.
##
## This program is distributed in the hope that it will be useful, but
## WITHOUT ANY WARRANTY; without even the implied warranty of
## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
## General Public License for more details.
##
## You should have received a copy of the GNU General Public License
## along with this file. If not, see <http://www.gnu.org/licenses/>.
## -*- texinfo -*-
## @deftypefn {Function File} {@var{lambda} =} eig (@var{KP})
## @deftypefnx{Function File} {[var{V}, @var{lambda}] =} eig (@var{KP})
## XXX: Write help text
## @seealso{eig, @kronprod/svd}
## @end deftypefn
function [V, lambda] = eig (KP, A)
## XXX: This implementation provides a different permutation of eigenvalues and
## eigenvectors compared to 'eig (full (KP))'
## Check input
if (nargin == 0 || nargin > 2)
print_usage ();
endif
if (!isa (KP, "kronprod"))
error ("eig: first input argument must be of class 'kronprod'");
endif
if (!issquare (KP))
error ("eig: first input must be a square matrix");
endif
## Take action
if (nargin == 1)
if (nargout <= 1)
## Only eigenvalues were requested
if (issquare (KP.A) && issquare (KP.B))
lambda_A = eig (KP.A);
lambda_B = eig (KP.B);
V = kronprod (lambda_A, lambda_B);
else
## We should be able to do this using SVD
error ("eig not implemented (yet) for Kronecker products of non-square matrices");
endif
elseif (nargout == 2)
## Both eigenvectors and eigenvalues were requested
if (issquare (KP.A) && issquare (KP.B))
[V_A, lambda_A] = eig (KP.A);
[V_B, lambda_B] = eig (KP.B);
V = kronprod (V_A, V_B);
lambda = kronprod (lambda_A, lambda_B);
else
## We should be able to do this using SVD
error ("eig not implemented (yet) for Kronecker products of non-square matrices");
endif
endif
elseif (nargin == 2)
## Solve generalised eigenvalue problem
## XXX: Is there a fancy way of doing this?
[V, lambda] = eig (full (KP), full (A));
endif
endfunction
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