Mauch MIREX 2010

function y = sample_node(CPD, pev, nsamples)

% SAMPLE_NODE Draw a random sample from P(Xi | x(pi_i), theta_i)  (tabular)

% Y = SAMPLE_NODE(CPD, PEV, NSAMPLES)

%

% pev(i,m) is the value of the i'th parent in sample m (if there are any parents).

% y(m) is the m'th sampled value (a row vector).

% (If pev is a cell array, so is y.)

% nsamples defaults to 1.

if nargin < 3, nsamples = 1; end

%if nargin < 4, usecell = 0; end

if iscell(pev), usecell = 1; else usecell = 0; end

if nsamples == 1, pev = pev(:); end

sz = CPD.sizes; 

nparents = length(sz)-1;

if nparents==0

  y = sample_discrete(CPD.CPT, 1, nsamples);

  if usecell

    y = num2cell(y);

  end

  return;

end

sz = CPD.sizes; 

[nparents nsamples] = size(pev);

if usecell

  pvals = cell2num(pev)'; % each row is a case

else

  pvals = pev';

end

psz = sz(1:end-1);

ssz = sz(end);

ndx = subv2ind(psz, pvals);

T = reshape(CPD.CPT, [prod(psz) ssz]);

T2 = T(ndx,:); % each row is a distribution selected by the parents

C = cumsum(T2, 2); % sum across columns

R = rand(nsamples, 1);

y = ones(nsamples, 1);

for i=1:ssz-1

  y = y + (R > C(:,i));

end

y = y(:)';

if usecell

  y = num2cell(y);

end