enter_soft_evidence.m

来自「Bayes网络工具箱」· M 代码 · 共 116 行

function [fwdback, loglik] = enter_soft_evidence(engine, CPDpot, filter)
% ENTER_SOFT_EVIDENCE Add soft evidence to network (frontier_fast)
% [fwdback, loglik] = enter_soft_evidence(engine, CPDpot, filter)

if nargin < 3, filter = 0; end

[ss T] = size(CPDpot);
bnet = bnet_from_engine(engine);
ns = repmat(bnet.node_sizes_slice(:), 1, T);
onodes = unroll_set(engine.onodes, ss, T);
ns(onodes)=1;
ns = ns(:)';

fengine = struct(engine.frontier_inf_engine); % violate privacy of object

% FORWARDS
fwd = cell(ss,T);
ll = zeros(1,T);
S = 2*ss; % num. intermediate frontiers to get from t to t+1
frontier = cell(S,T);


% Start with empty frontier, and add each node in slice 1
t = 1;
s = 1;
j = 1;
frontier{s,t} = CPDpot{j};
fwd{j} = frontier{s,t};
for s=2:ss
  j = s; % add node j at step s
  frontier{s,t} = frontier{s-1,t}(engine.fndx1{s}) .* CPDpot{j}(engine.CPD_ndx1{s});
  fwd{j} = frontier{s,t};
end
frontier{S,t} = frontier{ss,t};
[frontier{S,t}, lik] = normalise(frontier{S,t});
ll(t) = log(lik);

fndx = engine.fndx;
CPD_ndx = engine.CPD_ndx;

% Now move frontier from slice to slice
OPS = fengine.ops;
add = OPS>0;
nodes = [zeros(S,1) unroll_set(abs(OPS(:)), ss, T-1)];
for t=2:T
  for s=1:S
    if s==1
      prev_ndx = (t-2)*S + S; % S,t-1
    else
      prev_ndx = (t-1)*S + s-1; % s-1,t
    end
    j = nodes(s,t);
    if add(s)
      frontier{s,t} = frontier{prev_ndx}(fndx{s}) .* CPDpot{j}(CPD_ndx{s});
      fwd{j} = frontier{s,t};
    else
      frontier{s,t} = sum(frontier{prev_ndx}(fndx{s}), 2);
    end
  end
  [frontier{S,t}, lik] = normalise(frontier{S,t});
  ll(t) = log(lik);
end
loglik = sum(ll);

if filter
  fwdback = fwd;
  return;
end


% BACKWARDS
back = cell(ss,T);
add = ~add; % forwards add = backwards remove 
frontier = cell(S,T+1);
t = T;
frontier{1,T+1} = ones(prod(ns(1:ss)), 1);
CPD_ndx = engine.rev_CPD_ndx;
fndx = engine.rev_fndx;
for t=T:-1:2
  for s=S:-1:1 % reverse order
    if s==S
      prev_ndx = t*S + 1; % 1,t+1
    else
      prev_ndx = (t-1)*S + (s+1); % s+1,t
    end
    j = nodes(s,t);
    if ~add(s)
      back{j} = frontier{prev_ndx}; % save frontier before removing j
      frontier{prev_ndx} = frontier{prev_ndx} .* CPDpot{j}(CPD_ndx{s});
      frontier{s,t} = sum(frontier{prev_ndx}(fndx{s}), 2);
    else
      frontier{s,t} = frontier{prev_ndx}(fndx{s}); % copies elements
    end
  end
  frontier{1,t} = normalise(frontier{1,t});
end
% Remove each node in first slice until left with empty set
t = 1;
frontier{ss+1,t} = frontier{1,2};
for s=ss:-1:1
  j = s; % remove node j at step s
  back{j} = frontier{s+1,t};
  frontier{s+1,t} = frontier{s+1,t} .* CPDpot{j}(engine.rev_CPD_ndx1{s});
  frontier{s,t} = sum(frontier{s+1,t}(engine.rev_fndx1{s}), 2);
end

% COMBINE
fwdback = cell(ss,T);
for t=1:T
  for i=1:ss
   fwdback{i,t} = normalise(fwd{i,t}(:) .* back{i,t}(:));
  end
end