--- /dev/null
+## Copyright (C) 2006 Fredrik Bulow <fredrik.bulow@gmail.com>
+##
+## 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
+## this program; if not, see <http://www.gnu.org/licenses/>.
+
+## -*- texinfo -*-
+## @deftypefn {Function File} {} zigzag (@var{mtrx})
+## Returns zigzag walk-off of the elements of @var{mtrx}.
+## Essentially it walks the matrix in a Z-fashion.
+##
+## mat =
+## 1 4 7
+## 2 5 8
+## 3 6 9
+## then zigzag(mat) gives the output,
+## [1 2 4 7 5 3 6 8 9], by walking as
+## shown in the figure from pt 1 in that order of output.
+## The argument @var{mtrx} should be a MxN matrix
+##
+## An example of zagzig use:
+## @example
+## @group
+## mat = reshape(1:9,3,3);
+## zigzag(mat)
+## ans =[1 2 4 7 5 3 6 8 9]
+##
+## @end group
+## @end example
+##
+## @end deftypefn
+## @seealso{zagzig}
+
+function rval = zigzag(mtrx)
+ if nargin != 1
+ print_usage;
+ endif
+ n=size(mtrx);
+
+ if(issquare(mtrx)) #Square matrix (quick case)
+
+ ##We create a matrix of the same size as mtrx where odd elements are
+ ##1, others 0.
+ odd=kron(ones(ceil(n/2)),eye(2))((1:n(1)),(1:n(2)));
+
+ ##We transpose even elements only.
+ mtrx = mtrx.*odd + (mtrx.*(1-odd))';
+
+ ##Now we mirror the matrix. The desired vector is now the
+ ##concatenation of the diagonals.
+ mtrx=mtrx(:,1+size(mtrx,2)-(1:size(mtrx,2)));
+
+ ##Picking out the diagonals.
+ rval = [];
+ for i = n(2)-1:-1:1-n(1)
+ rval=[rval diag(mtrx,i)'];
+ endfor
+
+ else #Not square (Slow cases)
+ mtrx=mtrx(:,1+size(mtrx,2)-(1:size(mtrx,2)));
+
+ ##Picking out the diagonals and reversing odd ones manually.
+ rval = [];
+ for i = n(2)-1:-1:1-n(1)
+ new = diag(mtrx,i);
+ if(floor(i/2)==i/2) ##Even?
+ rval=[rval new'];
+ else ##Odd!
+ rval=[rval new((1+length(new))-(1:length(new)))'];
+ endif
+ endfor
+ endif
+endfunction
+
+%!assert(zigzag(reshape(1:9,3,3)),[1 2 4 7 5 3 6 8 9])