--- /dev/null
+## Copyright (C) 2010 VZLU Prague
+##
+## 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 of the License, 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 Octave; see the file COPYING. If not, see
+## <http://www.gnu.org/licenses/>.
+
+function ss = subsref (s, subs)
+ if (length (subs) != 1)
+ error ("blksparse: invalid index chain");
+ endif
+ if (strcmp (subs(1).type, "()"))
+ ind = subs(1).subs;
+ if (length (ind) == 2)
+ idx = make_block_index (ind{1}, s.bsiz(1));
+ jdx = make_block_index (ind{2}, s.bsiz(2));
+ ## Use sparse indexing to solve it all.
+ sn = sparse (s.i, s.j, 1:size (s.sv, 3), s.siz(1), s.siz (2));
+ sn = sn(idx, jdx);
+ [i, j, k] = find (sn);
+ ss = s;
+ ss.i = i;
+ ss.j = j;
+ ss.sv = s.sv(:,:,k);
+ ss.siz = size (sn);
+ else
+ error ("blksparse: linear indexing is not supported");
+ endif
+ else
+ error ("blksparse: only supports () indexing");
+ endif
+
+endfunction
+
+function bi = make_block_index (i, bs)
+ if (strcmp (i, ':'))
+ bi = i;
+ else
+ if (rem (numel (i), bs) == 0)
+ ba = reshape (i, bs, []);
+ bi = ba(1,:);
+ if (any (rem (bi, bs) != 1) || any ((ba != bsxfun (@plus, bi, [0:bs-1].'))(:)))
+ error ("blksparse: index must preserve block structure");
+ else
+ bi = ceil (bi / bs);
+ endif
+ else
+ error ("blksparse: index must preserve block structure");
+ endif
+ endif
+endfunction