comparison toolboxes/FullBNT-1.0.7/bnt/potentials/@cgpot/marginalize_pot.m @ 0:e9a9cd732c1e tip

first hg version after svn

+function smallpot = marginalize_pot(bigpot, keep, maximize, useC)
+% MARGINALIZE_POT Marginalize a cgpot onto a smaller domain.
+% smallpot = marginalize_pot(bigpot, keep, maximize, useC)
+%
+% If maximize = 1, we raise an error.
+% useC is ignored.
+
+if nargin < 3, maximize = 0; end
+assert(~maximize);
+
+
+sumover = mysetdiff(bigpot.domain, keep);
+csumover = myintersect(sumover, bigpot.cdom);
+dsumover = myintersect(sumover, bigpot.ddom);
+dkeep = myintersect(keep, bigpot.ddom);
+ckeep = myintersect(keep, bigpot.cdom);
+%ns = sparse(1, max(bigpot.domain)); % must be full, so I is an integer
+ns = zeros(1, max(bigpot.domain));
+ns(bigpot.ddom) = bigpot.dsizes;
+ns(bigpot.cdom) = bigpot.csizes;
+
+% sum(ns(csumover))==0 is like isempty(csumover) but handles observed nodes.
+% Similarly, prod(ns(dsumover))==1 is like isempty(dsumover)
+
+% Marginalize the cts parts.
+% If we are in canonical form, we stay that way, since moment form might not exist.
+% Besides, we would like to minimize the number of conversions.
+if sum(ns(csumover)) > 0
+  if bigpot.subtype == 'm'
+    for i=1:bigpot.dsize
+      bigpot.mom{i} = marginalize_pot(bigpot.mom{i}, ckeep);
+    end
+  else
+    for i=1:bigpot.dsize
+      bigpot.can{i} = marginalize_pot(bigpot.can{i}, ckeep);
+    end
+  end
+end
+
+% If we are not marginalizing over any discrete nodes, we are done.
+if prod(ns(dsumover))==1
+  smallpot = cgpot(dkeep, ckeep, ns, bigpot.can, bigpot.mom, bigpot.subtype);
+  return;
+end
+
+% To marginalize the discrete parts, we partition the cts parts into those that depend
+% on dkeep (i) and those that depend on on dsumover (j).
+
+I = prod(ns(dkeep));
+J = prod(ns(dsumover));
+C = sum(ns(ckeep));   
+sum_map = find_equiv_posns(dsumover, bigpot.ddom);
+keep_map = find_equiv_posns(dkeep, bigpot.ddom);
+iv = zeros(1, length(bigpot.ddom)); % index vector
+
+% If in canonical form, marginalize if possible, else convert to moment form.
+if 0 & bigpot.subtype == 'c'
+  p1 = zeros(I,J);
+  h1 = zeros(C,J,I);
+  K1 = zeros(C,C,J,I);
+  for i=1:I
+    keep_iv = ind2subv(ns(dkeep), i);
+    iv(keep_map) = keep_iv;
+    for j=1:J
+      sum_iv = ind2subv(ns(dsumover), j);
+      iv(sum_map) = sum_iv;
+      k = subv2ind(ns(bigpot.ddom), iv);
+      can = struct(bigpot.can{k}); % violate object privacy
+      p1(i,j) = exp(can.g);
+      if C > 0 % so mu1 and Sigma1 are non-empty
+	h1(:,j,i) = can.h;
+	K1(:,:,j,i) = can.K;
+      end
+    end
+  end
+  
+  % If the cts parts do not depend on j, we can just marginalize the weighting coefficient g.
+  jdepends = 0;
+  for i=1:I
+    for j=2:J
+      if ~approxeq(h1(:,j,i), h1(:,1,i)) | ~approxeq(K1(:,:,j,i), K1(:,:,1,i))
+	jdepends = 1;
+	break
+      end
+    end
+  end
+
+  if ~jdepends
+    %g2 = log(sum(p1, 2));
+    g2 = zeros(I,1);
+    for i=1:I
+      s = sum(p1(i,:));
+      if s > 0
+	g2(i) = log(s);
+      end
+    end
+    h2 = h1;
+    K2 = K1;
+    can = cell(1,I);
+    j = 1; % arbitrary
+    for i=1:I
+      can{i} = cpot(ckeep, ns(ckeep), g2(i), h2(:,j,i), K2(:,:,j,i));
+    end
+    smallpot = cgpot(dkeep, ckeep, ns, can, [], 'c');  
+    return;
+  else
+    % Since the cts parts depend on j, we must convert to moment form
+    bigpot = cg_can_to_mom(bigpot);
+  end
+end
+
+
+% Marginalize in moment form
+bigpot = cg_can_to_mom(bigpot);
+
+% Now partition the moment components.
+T1 = zeros(I,J);
+mu1 = zeros(C,J,I);
+Sigma1 = zeros(C,C,J,I);
+for i=1:I
+  keep_iv = ind2subv(ns(dkeep), i);
+  iv(keep_map) = keep_iv;
+  for j=1:J
+    sum_iv = ind2subv(ns(dsumover), j);
+    iv(sum_map) = sum_iv;
+    k = subv2ind(ns(bigpot.ddom), iv);
+    mom = struct(bigpot.mom{k}); % violate object privacy
+    T1(i,j) = exp(mom.logp);
+    if C > 0 % so mu1 and Sigma1 are non-empty
+      mu1(:,j,i) = mom.mu;
+      Sigma1(:,:,j,i) = mom.Sigma;
+    end
+  end
+end
+
+% Collapse the mixture of Gaussians
+coef = mk_stochastic(T1); % coef must be convex combination
+T2 = sum(T1,2);
+T2 = T2 + (T2==0)*eps;
+%if C > 0, disp('collapsing onto '); disp(leep); end
+mu = [];
+Sigma = [];
+mom = cell(1,I);
+for i=1:I
+  if C > 0
+    [mu, Sigma] = collapse_mog(mu1(:,:,i), Sigma1(:,:,:,i), coef(i,:));
+  end
+  logp = log(T2(i));
+  mom{i} = mpot(ckeep, ns(ckeep), logp, mu, Sigma);
+end
+
+smallpot = cgpot(dkeep, ckeep, ns, [], mom, 'm');
+