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Copyright Tristan Aubrey-Jones April 2007.
function probs = computeProbs(condVars, givenVars, conds, given)
% computeProbs computes the vector of probabilities
% for all the combinations of conditions and givens
% by directly manipulating the joint distribution.
% start
if (nargin == 2)
display('\begin{tabular}{c}');
probs = computeProbs(condVars, givenVars, [], []);
display('\end{tabular}');
else
% recursing through combinations
if (nargin == 4)
% check if all conditions are specified
szConds = size(conds);
szGiven = size(given);
if szConds(1) == length(condVars)
if szGiven(1) == length(givenVars)
% P(X|Y) = P(X,Y) / P(Y)
if szGiven(1) > 0
cs = conds;
for i = 1:szGiven(1)
cs(i + szConds(1), 1:2) = given(i, 1:2);
end
pXY = computeProb(cs);
pY = computeProb(given);
p = pXY ./ pY;
else
p = computeProb(conds);
end
probs = [p(1)];
% display in latex
sconds = condsToStr(conds);
sgiven = condsToStr(given);
display(sprintf(' $P(%s|%s) = %4.8f$\\\\', sconds, sgiven, probs));
else
% branch for current given
i = szGiven(1) + 1;
v = givenVars(i);
% when var is 1
given(i, 1:2) = [v 1];
probs = computeProbs(condVars, givenVars, conds, given);
% when var is 0
given(i, 1:2) = [v 0];
p2 = computeProbs(condVars, givenVars, conds, given);
sz = size(probs);
probs((sz(1)+1):(sz(1)*2), 1:sz(2)) = p2;
end
else
% branch for current cond
i = szConds(1) + 1;
v = condVars(i);
% when var is 1
conds(i, 1:2) = [v 1];
probs = computeProbs(condVars, givenVars, conds, given);
% when var is 0
conds(i, 1:2) = [v 0];
p2 = computeProbs(condVars, givenVars, conds, given);
sz = size(probs);
probs((sz(1)+1):(sz(1)*2), 1:sz(2)) = p2;
end
else
error('incorrect arguments.');
end
end