log_nextcase_prob_node.m

基于贝叶斯网络的源程序

function L = log_nextcase_prob_node(CPD, self_ev, pev, test_self_ev, test_pev)
% LOG_NEXTCASE_PROB_NODE compute the joint distribution of a node (tabular) of a new case given
% completely observed data.
%
% The input arguments are mainly similar with log_marg_prob_node(CPD, self_ev, pev, usecell),
% but add test_self_ev, test_pev, and without usecell
% test_self_ev(m) is the evidence on this node in a test case.
% test_pev(i) is the evidence on the i'th parent in the test case (if there are any parents).
%
% Written by [e-mail]

ncases = length(self_ev);
sz = CPD.sizes;
nparents = length(sz)-1;
assert(ncases == size(pev, 2)); 

if nargin < 6
  %usecell = 0;
  if iscell(self_ev)
    usecell = 1;
  else
    usecell = 0;
  end
end


if ncases==0
  L = 0;
  return;
elseif ncases==1  % speedup the sequential learning case; here need correction!!!
  CPT = CPD.CPT;
  % We assume the CPTs are already set to the mean of the posterior (due to bayes_update_params)
  if usecell
    x = cat(1, pev{:})';
    y = self_ev{1};
  else
    %x = pev(:)';
    x = pev;
    y = self_ev;
  end
  switch nparents
   case 0, p = CPT(y);
   case 1, p = CPT(x(1), y);
   case 2, p = CPT(x(1), x(2), y);
   case 3, p = CPT(x(1), x(2), x(3), y);
   otherwise,
    ind = subv2ind(sz, [x y]);
    p = CPT(ind);
  end
  L = log(p);
else
  % We ignore the CPTs here and assume the prior has not been changed
  
  % We arrange the data as in the following example.
  % Let there be 2 parents and 3 cases. Let p(i,m) be parent i in case m,
  % and y(m) be the child in case m. Then we create the data matrix
  % 
  % p(1,1) p(1,2) p(1,3)
  % p(2,1) p(2,2) p(2,3)
  % y(1)   y(2)   y(3)
  if usecell
    data = [cell2num(pev); cell2num(self_ev)]; 
  else
    data = [pev; self_ev];
  end
  counts = compute_counts(data, sz);
  
  % compute the (N_ijk'+ N_ijk)/(N_ij' + N_ij) under the condition of 1_m+1,ijk = 1 
  L = predict_family(counts, CPD.prior, test_self_ev, test_pev);
end