/usr/share/octave/packages/linear-algebra-2.2.0/@kronprod/inv.m is in octave-linear-algebra 2.2.0-1build1.
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 | ## 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} inv (@var{KP})
## Return the inverse of the Kronecker product @var{KP}.
##
## If @var{KP} is the Kronecker product of two square matrices @var{A} and @var{B},
## the inverse will be computed as the Kronecker product of the inverse of
## @var{A} and @var{B}.
##
## If @var{KP} is square but not a Kronecker product of square matrices, the
## inverse will be computed using the SVD
## @seealso{@@kronprod/sparse}
## @end deftypefn
function retval = inv (KP)
## Check input
if (nargin != 1)
print_usage ();
endif
if (!isa (KP, "kronprod"))
error ("inv: input argument must be of class 'kronprod'");
endif
## Do the computations
[n, m] = size (KP.A);
[q, r] = size (KP.B);
if (n == m && q == r) # A and B are both square
retval = kronprod (inv (KP.A), inv (KP.B));
elseif (n*q == m*r) # kron (A, B) is square
## We use the SVD to compute the inverse.
## XXX: Should we use 'eig' instead?
[U, S, V] = svd (KP);
retval = U * (1./S) * V';
else
error ("inv: argument must be a square matrix");
endif
endfunction
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