Add a useful package (from Source forge) for octave

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

diff --git a/octave_packages/linear-algebra-2.2.0/@kronprod/mldivide.m b/octave_packages/linear-algebra-2.2.0/@kronprod/mldivide.m
new file mode 100644 (file)
index 0000000..82cc42b
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+++ b/octave_packages/linear-algebra-2.2.0/@kronprod/mldivide.m
@@ -0,0 +1,59 @@
+## 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} mldivide (@var{M1}, @var{M2})
+## XXX: Write documentation
+## @end deftypefn
+
+function retval = mldivide (M1, M2)
+  ## Check input
+  if (nargin != 2)
+    print_usage ();
+  endif
+  
+  if (!ismatrix (M1) || !ismatrix (M2))
+    error ("mldivide: both input arguments must be matrices");
+  endif
+  
+  if (rows (M1) != rows (M2))
+    error ("mldivide: nonconformant arguments (op1 is %dx%d, op2 is %dx%d)",
+           rows (M1), columns (M1), rows (M2), columns (M2));
+  endif
+
+  ## Take action depending on types
+  M1_is_KP = isa (M1, "kronprod");
+  M2_is_KP = isa (M2, "kronprod");
+  
+  if (M1_is_KP && M2_is_KP) # Left division of Kronecker Products
+    error ("mldividide: this part not yet implemented as I'm lazy...");
+
+  elseif (M1_is_KP) # Left division of Kronecker Product and Matrix
+    ## XXX: Does this give the same minimum-norm solution as when using
+    ## XXX:   full (M1) \ M2
+    ## XXX: ? It is the same when M1 is invertible.
+    retval = zeros (columns (M1), columns (M2));
+    for n = 1:columns (M2)
+      M = reshape (M2 (:, n), [rows(M1.B), rows(M1.A)]);
+      retval (:, n) = vec ((M1.A \ (M1.B \ M)')');
+    endfor
+
+  elseif (M2_is_KP) # Left division of Matrix and Kronecker Product
+    error ("mldividide: this part not yet implemented as I'm lazy...");
+      
+  else
+    error ("mldivide: internal error for 'kronprod'");
+  endif
+endfunction