function C=som_connection(S)%SOM_CONNECTION Connection matrix for 'hexa' and 'rect' lattices%% C=som_connection(S)%%  C=som_connection(sMap);%  C=som_connection(sTopol);%  C=som_connection({'hexa', [6 5], 'sheet'});%% Input and output arguments:%  S    (struct) map or topol struct%       (cell array) a cell array of form {lattice, msize, shape}, where%                lattice: 'hexa' or 'rect'%                msize  : 1x2 vector%                shape  : 'sheet', 'cyl or 'toroid' %%  C    (sparse) An NxN connection matrix, N=prod(msize)%% The function returns a connection matrix, e.g., for drawing% connections between map units in the function som_grid. Note that% the connections are defined only in the upper triangular part to% save some memory!! Function SOM_UNIT_NEIGHS does the same thing, % but also has values in the lower triangular. It is also slower.%% For more help, try 'type som_connection' or check out online documentation.% See also SOM_GRID, SOM_UNIT_NEIGHS.%%%%%%%%%%%%% DETAILED DESCRIPTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% som_connection%% PURPOSE% %  To create a connection matrix of SOM 'hexa' and 'rect' negihborhoods%% SYNTAX%%  C = som_connection(S)%% DESCRIPTION%%  Creates a connection matrix of SOM 'hexa' and 'rect'%  neighborhoods. The connections are defined only in the upper%  triangular part to save some memory.%  %  Function SOM_UNIT_NEIGHS does the same thing, but also has values%  in the lower triangular. It is also slower, except for %  'toroid' shape because in that case this function calls %  SOM_UNIT_NEIGHS...%% REQUIRED INPUT ARGUMENTS%  %  S                 map topology %    (map struct)    S.topol is used to build the matrix%    (topol struct)  topology information is used to build the matrix%    (cell array)    of form {lattice, msize, shape}, where%                     lattice: 'hexa' or 'rect'%                     msize  : 1x2 vector%                     shape  : 'sheet', 'cyl or 'toroid' %% OUTPUT ARGUMENTS%%  C (sparse)        munits x munits sparse matrix which describes %                    nearest neighbor connections between units%% EXAMPLE %% C = som_connection('hexa',[3 4],'sheet');% full(C)% ans =%%      0     1     0     1     0     0     0     0     0     0     0     0%      0     0     1     1     1     1     0     0     0     0     0     0%      0     0     0     0     0     1     0     0     0     0     0     0%      0     0     0     0     1     0     1     0     0     0     0     0%      0     0     0     0     0     1     1     1     1     0     0     0%      0     0     0     0     0     0     0     0     1     0     0     0%      0     0     0     0     0     0     0     1     0     1     0     0%      0     0     0     0     0     0     0     0     1     1     1     1%      0     0     0     0     0     0     0     0     0     0     0     1%      0     0     0     0     0     0     0     0     0     0     1     0%      0     0     0     0     0     0     0     0     0     0     0     1%      0     0     0     0     0     0     0     0     0     0     0     0%% SEE ALSO% % som_grid         Visualization of a SOM grid% som_unit_neighs  Units in 1-neighborhood for all map units.% Copyright (c) 1999-2000 by the SOM toolbox programming team.% http://www.cis.hut.fi/projects/somtoolbox/             % Version 2.0alpha Johan 061099 juuso 151199 170400%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% Check argumentserror(nargchk(1, 1, nargin));   % check number of input arguments[tmp,ok,tmp]=som_set(S);if isstruct(S) & all(ok),       % check m type  switch S.type  case 'som_topol'     msize=S.msize;    lattice=S.lattice;    shape=S.shape;  case 'som_map'      msize=S.topol.msize;    lattice=S.topol.lattice;    shape=S.topol.shape;  otherwise    error('Invalid map or topol struct.');  endelseif iscell(S),  if vis_valuetype(S,{'topol_cell'}),    lattice=S{1};    msize=S{2};     shape=S{3};   else    error('{lattice, msize, shape} expected for cell input.')  endelse  error('{lattice, msize, shape}, or map or topol struct expected.')endif ~vis_valuetype(msize,{'1x2'})  error('Invalid map size: only 2D maps allowed.')end  %% Init %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%N=msize(1)*msize(2);%% Action & Build output arguments %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%switch latticecase 'hexa'  l1=ones(N,1); l1((msize(1)+1):msize(1):end)=0;  l2=zeros(msize(1),1); l3=l2;  l2(1:2:end-1)=1; l3(3:2:end)=1;  l2=repmat(l2,msize(2),1);   l3=repmat(l3,msize(2),1);  C= ...    spdiags([l1 l2 ones(N,1) l3], [1 msize(1)-1:msize(1)+1],N,N);case 'rect'  l1=ones(N,1);l1((msize(1)+1):msize(1):end)=0;  C=spdiags([l1 ones(N,1)],[1 msize(1)],N,N);otherwise  error('Unknown lattice.')endswitch shapecase 'sheet'  ;case 'cyl'  C=spdiags(ones(N,1),msize(1)*(msize(2)-1),C);case 'toroid'  %warning('Toroid not yet implemented: using ''cyl''.');  %C=spdiags(ones(N,1),msize(1)*(msize(2)-1),C);  %l=zeros(N,1); l(1:msize(2):end)=1;  %C=spdiags(l,msize(1),C);  % use som_unit_neighs to calculate these  C = som_unit_neighs(msize,lattice,'toroid');  % to be consistent, set the lower triangular values to zero  munits = prod(msize);  for i=1:(munits-1), C((i+1):munits,i) = 0; endotherwise  error('Unknown shape.');end