A neural network comprising discriminant function elements for calculating the inner product of an input pattern vector and a predetermined weighting vector to find similarity in order to accomplish hierarchical recognition of inputted patterns from a rough classification to a fine classification. The discriminant function element uses, as the weighting function described above, the vector (3) which is determined as the subtraction result of an arithmetic mean vector (reference vector) (22) of the pattern vectors as a whole belonging to the set as a reference on a pattern space from the result of addition of variation vectors (23) as variation of an arithmetic mean vector (target vector) (21) of all the pattern vectors to be determined, constitutes the variation vector again by using a random number generation process and a history vector limiting the upper limit of the random numbers generated in the random number generation process, and generates the identification function elements of 'offspring' by using the variation vector so constituted.
BIOLOGICAL NEURAL NETWORK