A model estimation device 100 includes a hidden variable variational probability calculation processing unit 104 for acquiring parameters of a hidden variable model and calculating a constrained hidden variable variational probability as a hidden variable posterior probability close to a previously-given distribution by use of the parameters, a model parameter optimization processing unit 105 for optimizing the parameters of the hidden variable model by use of the constrained hidden variable variational probability, and an optimality determination processing unit 106 for determining whether a marginalized log likelihood function using the optimized parameters is converged, wherein when it is determined that the marginalized log likelihood function is converged, the constrained hidden variable variational probability and the parameters used for the marginalized log likelihood function are output.
Please help me write a proper abstract based on the patent claims. CLAIM: 1. A model estimation device comprising: a hidden variable variational probability calculation processing unit which acquires parameters of a hidden variable model and calculating a constrained hidden variable variational probability as a hidden variable posterior probability close to a previously-given distribution by use of the parameters; a model parameter optimization processing unit which optimizes the parameters of the hidden variable model by use of the constrained hidden variable variational probability; and an optimality determination processing unit which determines whether a marginalized log likelihood function using the optimized parameters is converged, wherein when it is determined that the marginalized log likelihood function is not converged, the hidden variable variational probability calculation processing unit recalculates a constrained hidden variable variational probability by use of the optimized parameters, the model parameter optimization processing unit re-optimizes the parameters of the hidden variable model by use of the calculated constrained hidden variable variational probability, and when it is determined that the marginalized log likelihood function is converged, the constrained hidden variable variational probability and the parameters used for the marginalized log likelihood function are output. 2. The model estimation device according to claim 1, wherein the hidden variable variational probability calculation processing unit includes: a variational problem solution space calculation processing unit which calculates a presence range of a constrained hidden variable variational probability for increasing a lower bound of a marginalized log likelihood function; and a constrained variational problem calculation processing unit which calculates a constrained hidden variable variational probability close to a previously-given distribution from the presence range. 3. The model estimation device according to claim 1, comprising: a data input device which acquires candidates of the number of hidden states in a hidden variable model, and parameters of the hidden variable; a hidden state number setting unit which selects and sets the number of hidden states from among the acquired candidates of the number of hidden states; an initialization processing unit which initializes the parameters and a constrained hidden variable variational probability; an optimum model selection processing unit which, when a marginalized log likelihood function based on the parameters optimized by the model parameter optimization processing unit is larger than a currently-set marginalized log likelihood function, sets a model indicated by the larger marginalized log likelihood function as an optimum model; and a model estimation result output device which outputs a model estimation result including a constrained hidden variable variational probability and parameters of the optimum model, wherein when a non-optimized candidate of the number of hidden states is present, the hidden state number setting unit sets the non-optimized candidate of the number of hidden states as the number of hidden states, the initialization processing unit re-initializes the parameters and the constrained hidden variable variational probability, the hidden variable variational probability calculation processing unit recalculates a constrained hidden variable variational probability, the model parameter optimization processing unit re-optimizes the parameters of the hidden variable model, and the optimality determination processing unit re-determines whether the marginalized log likelihood function is converged. 4. The model estimation device according to claim 1, comprising: a gate function optimization processing unit which optimizes parameters of a branch node in a hierarchical hidden structure expressing a hidden variable and having a plurality of hierarchies, wherein the hidden variable variational probability calculation processing unit calculates a path hidden variable variational probability as a path hidden variable posterior probability indicating a correspondence between an observation variable and a component configuring a hidden variable model per hierarchy, the model parameter optimization processing unit acquires an observation probability type of the hidden variable model, and optimizes the parameters and the observation probability type of each component in the hidden variable model, and the optimality determination processing unit determines whether an optimization reference as a lower bound of a marginalized log likelihood function using the optimized parameters and the observation probability type is converged. 5. The model estimation device according to claim 4, wherein the hidden variable variational probability calculation processing unit includes: a variational problem solution space calculation processing unit which calculates a presence range of a lowermost layer path hidden variable variational probability for increasing an optimization reference; a constrained lowermost layer path hidden variable variational probability calculation processing unit which assumes a closest probability to a previously-given distribution from among the presence range of the lowermost layer path hidden variable variational probability as an updated value of the lowermost layer path hidden variable variational probability; a hierarchy setting unit which sets one layer above a immediately-previous layer to be calculate as a layer to be calculated; an upper layer path hidden variable variational probability calculation processing unit which takes a sum of the lowermost layer constrained hidden variable variational probabilities that the layer has a same branch nodes as a parent node and the layer is in a current layer to be calculated, and assumes the sum as a path hidden variable variational probability in one layer above; and a hierarchical calculation end determination processing unit which confirms whether there is a layer for which the path hidden variable variational probability is not completely calculated, and confirms whether to terminate the calculation. 6. The model estimation device according to claim 4, wherein the gate function optimization processing unit includes: a branch node information acquisition unit which acquires information on branch nodes in a hidden variable model of optimized parameters; a branch node selection processing unit which selects a branch node to be optimized from among the acquired branch nodes; a branch parameter optimization processing unit which optimizes a branch parameter in the selected branch node by use of a path hidden variable variational probability calculated by the hidden variable variational probability calculation processing unit; and an all-branch node optimization end determination processing unit which determines whether all the acquired branch nodes are optimized. 7. The model estimation device according to claim 4, comprising: a data input device which acquires parameters of a hidden variable model including candidates of a hierarchical hidden structure indicating a hidden variable, an observation probability type, and candidates of the number of components; a hierarchical hidden structure setting unit which selects and sets one candidate of the candidates of the hierarchical hidden structure; an initialization processing unit which initializes the observation probability type, parameters of the observation probability, a hidden variable, and a lowermost layer path hidden variable variational probability of the hidden variable; an optimum model selection processing unit which, when an optimization reference based on the parameters optimized by the model parameter optimization processing unit is larger than a currently-set optimization reference, sets a model indicated by a marginalized log likelihood function based on the parameters optimized by the model parameter optimization processing unit as an optimum model; and a model estimation result output device which outputs a model estimation result including a constrained hidden variable variational probability and parameters in the optimum model, wherein when a non-optimized candidate of the hierarchical hidden structure is present, the hierarchical hidden structure setting unit sets the non-optimized candidate of the hierarchical hidden structure as a hierarchical hidden structure to be calculated, the initialization processing unit re-initializes, the hidden variable variational probability calculation processing unit recalculates a path hidden variable variational probability, the model parameter optimization processing unit re-optimizes the parameters of each component and the observation probability type in the hidden variable model, and the optimality determination processing unit determines whether an optimization reference as a lower bound of the marginalized log likelihood function is converged. 8. A model estimation method comprising: acquiring parameters of a hidden variable model and calculating a constrained hidden variable variational probability as a hidden variable posterior probability close to a previously-given distribution by use of the parameters; optimizing the parameters of the hidden variable model by use of the constrained hidden variable variational probability; determining whether a marginalized log likelihood function using the optimized parameters is converged, when it is determined that the marginalized log likelihood function is not converged, recalculating a constrained hidden variable variational probability by use of the optimized parameters, re-optimizing the parameters of the hidden variable model by use of the calculated constrained hidden variable variational probability, and when it is determined that the marginalized log likelihood function is converged, outputting the constrained hidden variable variational probability and the parameters used for the marginalized log likelihood function. 9. A non-transitory computer readable information recording medium storing a model estimation program that, when executed by a processor, performs a method for: acquiring parameters of a hidden variable model and calculating a constrained hidden variable variational probability as a hidden variable posterior probability close to a previously-given distribution by use of the parameters; optimizing the parameters of the hidden variable model by use of the constrained hidden variable variational probability; determining whether a marginalized log likelihood function using the optimized parameters is converged, when it is determined that the marginalized log likelihood function is not converged, recalculating a constrained hidden variable variational probability by use of the optimized parameters, re-optimizing the parameters of the hidden variable model by use of the calculated constrained hidden variable variational probability, and when it is determined that the marginalized log likelihood function is converged, outputting the constrained hidden variable variational probability and the parameters used for the marginalized log likelihood function.