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;endCPD = init_fields;if nargin < 3, val = []; endns = bnet.node_sizes;ps = parents(bnet.dag, self);if ~isempty(ps)  error('root CPDs should have no parents')endCPD.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 = [];