A hierarchical latent structure setting unit 81 sets a hierarchical latent structure that is a structure in which latent variables are represented by a tree structure and components representing probability models are located at nodes of a lowest level of the tree structure. A variational probability computation unit 82 computes a variational probability of a path latent variable that is a latent variable included in a path linking a root node to a target node in the hierarchical latent structure. A component optimization unit 83 optimizes each of the components for the computed variational probability. A gating function optimization unit 84 optimizes a gating function model that is a model for determining a branch direction according to the multivariate data in a node of the hierarchical latent structure, on the basis of the variational probability of the latent variable in the node.
Please help me write a proper abstract based on the patent claims. CLAIM: 1. A hierarchical latent variable model estimation apparatus for estimating a hierarchical latent variable model for multivariate data, the hierarchical latent variable model estimation apparatus comprising: a hierarchical latent structure setting unit for setting a hierarchical latent structure that is a structure in which latent variables are represented by a tree structure and components representing probability models are located at nodes of a lowest level of the tree structure; a variational probability computation unit for computing a variational probability of a path latent variable that is a latent variable included in a path linking a root node to a target node in the hierarchical latent structure; a component optimization unit for optimizing each of the components for the computed variational probability; and a gating function optimization unit for optimizing a gating function model that is a model for determining a branch direction according to the multivariate data in a node of the hierarchical latent structure, on the basis of the variational probability of the latent variable in the node. 2. The hierarchical latent variable model estimation device according to claim 1, comprising a hierarchical latent structure optimization unit for optimizing the hierarchical latent structure by removing, from the model, a path whose computed variational probability is equal to or less than a predetermined threshold. 3. The hierarchical latent variable model estimation device according to claim 2, wherein the gating function optimization unit includes: an effective branch node selection unit for selecting an effective branch node from nodes of the hierarchical latent structure, the effective branch node being a branch node of a path not removed from the hierarchical latent structure; and a gating function optimization parallel processing unit for optimizing the gating function model on the basis of the variational probability of the latent variable in the effective branch node, and wherein the gating function optimization parallel processing unit performs optimization of each branch parameter for the effective branch node in parallel. 4. The hierarchical latent variable model estimation device according to claim 1, wherein the hierarchical latent structure setting unit sets the hierarchical latent structure in which the latent variables are represented by a binary tree structure, and wherein the gating function optimization unit optimizes the gating function model based on a Bernoulli distribution, on the basis of the variational probability of the latent variable in the node. 5. The hierarchical latent variable model estimation device according to claim 1, wherein the variational probability computation unit computes the variational probability of the path latent variable of the lowest level so as to maximize an optimization criterion computed on the basis of the path latent variable of the lowest level and a parameter of a component, and computes a sum of computed variational probabilities of path latent variables of the level as the variational probability of the path latent variable of a higher level, on a level-by-level basis. 6. A computer implemented hierarchical latent variable model estimation method for estimating a hierarchical latent variable model for multivariate data, the hierarchical latent variable model estimation method comprising: setting a hierarchical latent structure that is a structure in which latent variables are represented by a tree structure and components representing probability models are located at nodes of a lowest level of the tree structure; computing a variational probability of a path latent variable that is a latent variable included in a path linking a root node to a target node in the hierarchical latent structure; optimizing each of the components for the computed variational probability; and optimizing a gating function model that is a model for determining a branch direction according to the multivariate data in a node of the hierarchical latent structure, on the basis of the variational probability of the latent variable in the node. 7. The hierarchical latent variable model estimation method according to claim 6, comprising optimizing the hierarchical latent structure by removing, from the model, a path whose computed variational probability is equal to or less than a predetermined threshold. 8. A non-transitory computer-readable recording medium having recorded thereon a hierarchical latent variable model estimation program for estimating a hierarchical latent variable model for multivariate data, the hierarchical latent variable model estimation program causing a computer to execute: a hierarchical latent structure setting process of setting a hierarchical latent structure that is a structure in which latent variables are represented by a tree structure and components representing probability models are located at nodes of a lowest level of the tree structure; a variational probability computation process of computing a variational probability of a path latent variable that is a latent variable included in a path linking a root node to a target node in the hierarchical latent structure; a component optimization process of optimizing each of the components for the computed variational probability; and a gating function optimization process of optimizing a gating function model that is a model for determining a branch direction according to the multivariate data in a node of the hierarchical latent structure, on the basis of the variational probability of the latent variable in the node. 9. The recording medium according to claim 8, wherein the hierarchical latent variable model estimation program causes the computer to execute a hierarchical latent structure optimization process of optimizing the hierarchical latent structure by removing, from the model, a path whose computed variational probability is equal to or less than a predetermined threshold.