% Hessian of the measurement function in BOT-demo.% Copyright (C) 2007 Jouni Hartikainen%% This software is distributed under the GNU General Public % Licence (version 2 or later); please refer to the file % Licence.txt, included with the software, for details.function dY = bot_d2h_dx2(x,s)  % Space for Hessians. Note that we need a Hessian for  % each dimension in the measurement space, that is we need  % a Hessian for each sensor in this case.       dY = zeros(size(s,2),size(x,1),size(x,1));    % Loop through sensors.  for i=1:size(s,2)    % Derivative twice wrt. x    dx2 = -2*(x(1)-s(1,i)) / ((x(1)-s(1,i))^2+(x(2)-s(2,i))^2)^2;    % Derivative twice wrt. y        dy2 = -2*(x(2)-s(2,i)) / ((x(1)-s(1,i))^2+(x(2)-s(2,i))^2)^2;    % Derivative wrt. x and y    dxdy = ((x(2)-s(2,i))^2-(x(1)-s(1,i))^2) / ((x(1)-s(1,i))^2+(x(2)-s(2,i))^2)^2;    dh = [dx2  dxdy 0 0;...	  dxdy dy2  0 0;...	  0    0    0 0;...          0    0    0 0];    dY(i,:,:) = dh;  end