9. An article of manufacture, comprising: a computer usable medium having computer readable program code means embodied therein for causing a computer to function as a model adaptation system in a pattern recognition in which a likelihood of an input vector with respect to each probabilistic model expressing features of each recognition category is calculated and a recognition category expressed by a probabilistic model with a highest likelihood among a plurality of prescribed probabilistic models is outputted as a recognition result, the computer readable program code means including: first a computer readable program code means for causing said computer to train an initial condition probabilistic model from a parameter expressing a condition of pattern recognition and probabilistic model training which is recorded at a time of model training; second computer readable program code means for causing said computer to obtain an initial condition imposed probabilistic models from the initial condition probabilistic model and prescribed reference probabilistic models corresponding to a prescribed value of the parameter expressing the condition; third computer readable program code means for causing said computer to calculate and store Jacobian matrices of a Taylor expansion expressing a change in a model parameter in terms of a change in the parameter expressing the condition, from the initial condition probabilistic model and the initial condition imposed probabilistic models; fourth computer readable program code means for causing said computer to train an adaptation target condition probabilistic model by using the parameter expressing the condition which is observed at a time of actual recognition; and fifth computer readable program code means for causing said computer to obtain an adapted condition imposed probabilistic models by updating the initial condition imposed probabilistic models according to the Taylor expansion using the Jacobian matrices, when the initial condition probabilistic model and the adaptation target condition probabilistic model are mismatching.
9. An article of manufacture, comprising: a computer usable medium having computer readable program code means embodied therein for causing a computer to function as a model adaptation system in a pattern recognition in which a likelihood of an input vector with respect to each probabilistic model expressing features of each recognition category is calculated and a recognition category expressed by a probabilistic model with a highest likelihood among a plurality of prescribed probabilistic models is outputted as a recognition result, the computer readable program code means including: first a computer readable program code means for causing said computer to train an initial condition probabilistic model from a parameter expressing a condition of pattern recognition and probabilistic model training which is recorded at a time of model training; second computer readable program code means for causing said computer to obtain an initial condition imposed probabilistic models from the initial condition probabilistic model and prescribed reference probabilistic models corresponding to a prescribed value of the parameter expressing the condition; third computer readable program code means for causing said computer to calculate and store Jacobian matrices of a Taylor expansion expressing a change in a model parameter in terms of a change in the parameter expressing the condition, from the initial condition probabilistic model and the initial condition imposed probabilistic models; fourth computer readable program code means for causing said computer to train an adaptation target condition probabilistic model by using the parameter expressing the condition which is observed at a time of actual recognition; and fifth computer readable program code means for causing said computer to obtain an adapted condition imposed probabilistic models by updating the initial condition imposed probabilistic models according to the Taylor expansion using the Jacobian matrices, when the initial condition probabilistic model and the adaptation target condition probabilistic model are mismatching. 10. The article of manufacture of claim 9, wherein a preliminary processing realized by the first, second and third computer readable program code means is carried out in advance, prior to an adaptation processing realized by the fourth and fifth computer readable program code means which is carried out at a time of actual recognition.