Mauch MIREX 2010

function CPD = root_CPD(bnet, self, val)

% ROOT_CPD Make a conditional prob. distrib. which has no parameters.

% CPD = ROOT_CPD(BNET, NODE_NUM, VAL)

%

% The node must not have any parents and is assumed to always be observed.

% It is a way of modelling exogenous inputs to a model.

% VAL is the value to which the root is clamped (default: [])

if nargin==0

  % This occurs if we are trying to load an object from a file.

  CPD = init_fields;

  CPD = class(CPD, 'root_CPD', generic_CPD(1));

  return;

elseif isa(bnet, 'root_CPD')

  % This might occur if we are copying an object.

  CPD = bnet;

  return;

end

CPD = init_fields;

if nargin < 3, val = []; end

ns = bnet.node_sizes;

ps = parents(bnet.dag, self);

if ~isempty(ps)

  error('root CPDs should have no parents')

end

CPD.self = self;

CPD.val = val;

CPD.sizes = ns(self);

clamped = 1;

CPD = class(CPD, 'root_CPD', generic_CPD(clamped));

%%%%%%%%%%%

function CPD = init_fields()

% This ensures we define the fields in the same order 

% no matter whether we load an object from a file,

% or create it from scratch. (Matlab requires this.)

CPD.self = [];

CPD.val = [];

CPD.sizes = [];