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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 = [];
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