HMM语音识别_HMM模型matlab编程包含前向后向算法实现.zip

function [loglik, gamma] = fhmm_infer(inter, CPTs_slice1, CPTs, obsmat, node_sizes) % FHMM_INFER Exact inference for a factorial HMM. % [loglik, gamma] = fhmm_infer(inter, CPTs_slice1, CPTs, obsmat, node_sizes) % % Inputs: % inter - the inter-slice adjacency matrix % CPTs_slice1{s}(j) = Pr(Q(s,1) = j) where Q(s,t) = hidden node s in slice t % CPT{s}(i1, i2, ..., j) = Pr(Q(s,t) = j | Pa(s,t-1) = i1, i2, ...), % obsmat(i,t) = Pr(y(t) | Q(t)=i) % node_sizes is a vector with the cardinality of the hidden nodes % % Outputs: % gamma(i,t) = Pr(X(t)=i | O(1:T)) as in an HMM, % except that i is interpreted as an M digit, base-K number (if there are M chains each of cardinality K). % % This function implements the frontier algorithm, as described in % "A Forward-Backward Algorithm for Inference in Bayesian Networks and An Empirical Comparison with HMMs" % G. Zweig, Master's Thesis. UC Berkeley, 1996. % The frontier algorithm is an extension of the one in appendix B of % Ghahramani and Jordan, "Factorial Hidden Markov Models", Machine Learning 29:245--273, 1997. % % For M chains each of cardinality K, the frontiers (i.e., cliques) % contain M+1 nodes, and it takes M steps to advance the frontier by one time step, % so the run time is O(T M K^(M+1)). % An HMM takes O(T S^2) where S is the size of the state space. % Collapsing the FHMM to an HMM results in S = K^M. % % The frontier algorithm makes the following topological assumptions: % % - All nodes are persistent (connect to the next slice) % - No connections within a timeslice % - There is a single observation variable, which depends on all the hidden nodes % - Each node can have several parents in the previous time slice (generalizes a FHMM slightly) % % The forwards pass of the frontier algorithm can be explained with the following example. % Suppose we have 3 hidden nodes per slice, A, B, C. % The goal is to compute alpha(j, t) = Pr( (A_t,B_t,C_t)=j , Y_1:t) % We move alpha from t to t+1 one node at a time, as follows. % a(j,1) = Pr( (A_t,B_t,C_t)=j , Y_1:t) = alpha(j,t) % a(j,2) = Pr( (A_t+1,B_t,C_t)=j , Y_1:t) = sum_{aold} Pr( A_t+1=anew | Parents = k) * Pr((A_t,B_t,C_t)=k , Y_1:t) % where k=j except A_t+1=anew in j and A_t=aold in k, and Pr((A_t,B_t,C_t)=k , Y_1:t) = a(k,1) % a(j,3) = Pr( (A_t+1,B_t+1,C_t)=j , Y_1:t) = sum_{bold} Pr( B_t+1=bnew | Pa = k) * Pr((A_t+1,B_t,C_t)=k , Y_1:t) % a(j,4) = Pr( (A_t+1,B_t+1,C_t+1)=j , Y_1:t) = sum_{cold} Pr( C_t+1=cnew | Pa = k) * Pr((A_t+1,B_t+1,C_t)=k , Y_1:t) % alpha(j,t+1) = Pr( (A_t+1,B_t+1,C_t+1)=j , Y_1:t+1) = a(j,4) * Pr(Y_t+1 | (A_t+1,B_t+1,C_t+1)=j ) [kk,ll,mm] = make_frontier_indices(inter, node_sizes); % can pass in as args scaled = 1; M = length(node_sizes); S = prod(node_sizes); T = size(obsmat, 2); alpha = zeros(S, T); beta = zeros(S, T); gamma = zeros(S, T); scale = zeros(1,T); tiny = exp(-700); alpha(:,1) = make_prior_from_CPTs(CPTs_slice1, node_sizes); alpha(:,1) = alpha(:,1) .* obsmat(:, 1); if scaled s = sum(alpha(:,1)); if s==0, s = s + tiny; end scale(1) = 1/s; else scale(1) = 1; end alpha(:,1) = alpha(:,1) * scale(1); %a = zeros(S, M+1); %b = zeros(S, M+1); anew = zeros(S,1); aold = zeros(S,1); bnew = zeros(S,1); bold = zeros(S,1); for t=2:T %a(:,1) = alpha(:,t-1); aold = alpha(:,t-1); c = 1; for i=1:M ns = node_sizes(i); cpt = CPTs{i}; for j=1:S s = 0; for xx=1:ns %k = kk(xx,j,i); %l = ll(xx,j,i); k = kk(c); l = ll(c); c = c + 1; % s = s + a(k,i) * CPTs{i}(l); s = s + aold(k) * cpt(l); end %a(j,i+1) = s; anew(j) = s; end aold = anew; end %alpha(:,t) = a(:,M+1) .* obsmat(:, obs(t)); alpha(:,t) = anew .* obsmat(:, t); if scaled s = sum(alpha(:,t)); if s==0, s = s + tiny; end scale(t) = 1/s; else scale(t) = 1; end alpha(:,t) = alpha(:,t) * scale(t); end beta(:,T) = ones(S,1) * scale(T); for t=T-1:-1:1 %b(:,1) = beta(:,t+1) .* obsmat(:, obs(t+1)); bold = beta(:,t+1) .* obsmat(:, t+1); c = 1; for i=1:M ns = node_sizes(i); cpt = CPTs{i}; for j=1:S s = 0; for xx=1:ns %k = kk(xx,j,i); %m = mm(xx,j,i); k = kk(c); m = mm(c); c = c + 1; % s = s + b(k,i) * CPTs{i}(m); s = s + bold(k) * cpt(m); end %b(j,i+1) = s; bnew(j) = s; end bold = bnew; end % beta(:,t) = b(:,M+1) * scale(t); beta(:,t) = bnew * scale(t); end if scaled loglik = -sum(log(scale)); % scale(i) is finite else lik = alpha(:,1)' * beta(:,1); loglik = log(lik+tiny); end for t=1:T gamma(:,t) = normalise(alpha(:,t) .* beta(:,t)); end %%%%%%%%%%% function [kk,ll,mm] = make_frontier_indices(inter, node_sizes) % % Precompute indices for use in the frontier algorithm. % These only depend on the topology, not the parameters or data. % Hence we can compute them outside of fhmm_infer. % This saves a lot of run-time computation. M = length(node_sizes); S = prod(node_sizes); mns = max(node_sizes); kk = zeros(mns, S, M); ll = zeros(mns, S, M); mm = zeros(mns, S, M); for i=1:M for j=1:S u = ind2subv(node_sizes, j); x = u(i); for xx=1:node_sizes(i) uu = u; uu(i) = xx; k = subv2ind(node_sizes, uu); kk(xx,j,i) = k; ps = find(inter(:,i)==1); ps = ps(:)'; l = subv2ind(node_sizes([ps i]), [uu(ps) x]); % sum over parent ll(xx,j,i) = l; m = subv2ind(node_sizes([ps i]), [u(ps) xx]); % sum over child mm(xx,j,i) = m; end end end %%%%%%%%% function prior=make_prior_from_CPTs(indiv_priors, node_sizes) % % composite_prior=make_prior(individual_priors, node_sizes) % Make the prior for the first node in a Markov chain % from the priors on each node in the equivalent DBN. % prior{i}(j) = Pr(X_i=j), where X_i is the i'th node in slice 1. % composite_prior(i) = Pr(slice1 = i). n = length(indiv_priors); S = prod(node_sizes); prior = zeros(S,1); for i=1:S vi = ind2subv(node_sizes, i); p = 1; for k=1:n p = p * indiv_priors{k}(vi(k)); end prior(i) = p; end %%%%%%%%%%% function [loglik, alpha, beta] = FHMM_slow(inter, CPTs_slice1, CPTs, obsmat, node_sizes, data) % % Same as the above, except we don't use the optimization of computing the indices outside the loop. scaled = 1; M = length(node_sizes); S = prod(node_sizes); [numex T] = size(data); obs = data; alpha = zeros(S, T); beta = zeros(S, T); a = zeros(S, M+1); b = zeros(S, M+1); scale = zeros(1,T); alpha(:,1) = make_prior_from_CPTs(CPTs_slice1, node_sizes); alpha(:,1) = alpha(:,1) .* obsmat(:, obs(1)); if scaled s = sum(alpha(:,1)); if s==0, s = s + tiny; end scale(1) = 1/s; else scale(1) = 1; end alpha(:,1) = alpha(:,1) * scale(1); for t=2:T fprintf(1, 't %d\n', t); a(:,1) = alpha(:,t-1); for i=1:M for j=1:S u = ind2subv(node_sizes, j); xnew = u(i); s = 0; for xold=1:node_sizes(i) uold = u; uold(i) = xold; k = subv2ind(node_sizes, uold); ps = find(inter(:,i)==1); ps = ps(:)'; l = subv2ind(node_sizes([ps i]), [uold(ps) xnew]); s = s + a(k,i) * CPTs{i}(l); end a(j,i+1) = s; end end alpha(:,t) = a(:,M+1) .* obsmat(:, obs(t)); if scaled s = sum(alpha(:,t)); if s==0, s = s + tiny; end scale(t) = 1/s; else scale(t) = 1; end alpha(:,t) = alpha(:,t) * scale(t); end beta(:,T) = ones(S,1) * scale(T); for t=T-1:-1:1 fprintf(1, 't %d\n', t); b(:,1) = beta(:,t+1) .* obsmat(:, obs(t+1)); for i=1:M for j=1:S u = ind2subv(node_sizes, j); xold = u(i); s = 0; for xnew=1:node_sizes(i) unew = u; unew(i) = xnew; k = subv2ind(node_sizes, unew); ps = find(inter(:,i)==1); ps = ps(:)'; l = subv2ind(node_sizes([ps i]), [u(ps) xnew]); s = s + b(k,i) * CPTs{i}(l); end b(j,i+1) = s; end end beta(:,t) = b(:,M+1) * scale(t); end if scaled loglik = -sum(log(scale)); % scale(i) is finite else lik = alpha(:,1)' * beta(:,1); loglik = log(lik+tiny); end