Add a useful package (from Source forge) for octave

[CreaPhase.git] / octave_packages / linear-algebra-2.2.0 / @kronprod / not_done / eig.m

diff --git a/octave_packages/linear-algebra-2.2.0/@kronprod/not_done/eig.m b/octave_packages/linear-algebra-2.2.0/@kronprod/not_done/eig.m
new file mode 100644 (file)
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+++ b/octave_packages/linear-algebra-2.2.0/@kronprod/not_done/eig.m
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+## Copyright (C) 2010  Soren Hauberg
+## 
+## 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