Add a useful package (from Source forge) for octave

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

diff --git a/octave_packages/linear-algebra-2.2.0/@kronprod/mtimes.m b/octave_packages/linear-algebra-2.2.0/@kronprod/mtimes.m
new file mode 100644 (file)
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+++ b/octave_packages/linear-algebra-2.2.0/@kronprod/mtimes.m
@@ -0,0 +1,92 @@
+## 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} mtimes (@var{KP})
+## XXX: Write documentation
+## @end deftypefn
+
+function retval = mtimes (M1, M2)
+  ## Check input
+  if (nargin == 0)
+    print_usage ();
+  elseif (nargin == 1)
+    ## This seems to be what happens for full and sparse matrices, so we copy this behaviour
+    retval = M1;
+    return;
+  endif
+  
+  if (!ismatrix (M1) || !ismatrix (M2))
+    error ("mtimes: input arguments must be matrices");
+  endif
+  
+  if (columns (M1) != rows (M2))
+    error ("mtimes: nonconformant arguments (op1 is %dx%d, op2 is %dx%d)",
+           rows (M1), columns (M1), rows (M2), columns (M2));
+  endif
+
+  ## Take action depending on input types
+  M1_is_KP = isa (M1, "kronprod");
+  M2_is_KP = isa (M2, "kronprod");
+  
+  if (M1_is_KP && M2_is_KP) # Product of Kronecker Products
+    ## Check if the size match such that the result is a Kronecker Product
+    if (columns (M1.A) == rows (M2.A) && columns (M1.B) == rows (M2.B))
+      retval = kronprod (M1.A * M2.A, M1.B * M2.B);
+    else
+      ## Form the full matrix of the smallest matrix and use that to compute the
+      ## final product
+      ## XXX: Can we do something smarter here?
+      numel1 = numel (M1);
+      numel2 = numel (M2);
+      if (numel1 < numel2)
+        retval = full (M1) * M2;
+      else
+        retval = M1 * full (M2);
+      endif
+    endif
+    
+  elseif (M1_is_KP && isscalar (M2)) # Product of Kronecker Product and scalar
+    if (numel (M1.A) < numel (M1.B))
+      retval = kronprod (M2 * M1.A, M1.B);
+    else
+      retval = kronprod (M1.A, M2 * M1.B);
+    endif
+    
+  elseif (M1_is_KP && ismatrix (M2)) # Product of Kronecker Product and Matrix
+    retval = zeros (rows (M1), columns (M2));
+    for n = 1:columns (M2)
+      M = reshape (M2 (:, n), [columns(M1.B), columns(M1.A)]);
+      retval (:, n) = vec (M1.B * M * M1.A');
+    endfor
+  
+  elseif (isscalar (M1) && M2_is_KP) # Product of scalar and Kronecker Product
+    if (numel (M2.A) < numel (M2.B))
+      retval = kronprod (M1 * M2.A, M2.B);
+    else
+      retval = kronprod (M2.A, M1 * M2.B);
+    endif
+    
+  elseif (ismatrix (M1) && M2_is_KP) # Product of Matrix and Kronecker Product
+    retval = zeros (rows (M1), columns (M2));
+    for n = 1:rows (M1)
+      M = reshape (M1 (n, :), [rows(M2.B), rows(M2.A)]);
+      retval (n, :) = vec (M2.B' * M * M2.A);
+    endfor
+      
+  else
+    error ("mtimes: internal error for 'kronprod'");
+  endif
+endfunction