1. An information processing apparatus comprising: an acquisition unit configured to acquire a multidimensional input vector; a derivation unit configured to derive, for each dimension of the input vector, a function value of a single-variable function with an element of the dimension as a variable, by referring to a lookup table indicating a correspondence between a variable and a function value of the single-variable function, wherein a product of the single-variable functions approximates a function value of a multiple-variable function; a product calculation unit configured to calculate, for each dimension of the input vector, a product of the function value derived by the derivation unit and a predetermined coefficient corresponding to the dimension; and an output unit configured to output a value calculated using the total of the products calculated by the product calculation unit for each dimension of the input vector as a classification index indicating a class of the input vector.