13. The apparatus of claim 10, in which the writer-specific reference vector generating means includes: means for predicting, from the feature vector of each selected input character, a writer-specific feature vector for the at least one category different from the candidate category to which the selected input character belongs; and reference vector correcting means, operating in response to the writer-specific feature vector for each category, for correcting the reference vector for the category to obtain the writer-specific reference vector for the category.
13. The apparatus of claim 10, in which the writer-specific reference vector generating means includes: means for predicting, from the feature vector of each selected input character, a writer-specific feature vector for the at least one category different from the candidate category to which the selected input character belongs; and reference vector correcting means, operating in response to the writer-specific feature vector for each category, for correcting the reference vector for the category to obtain the writer-specific reference vector for the category. 14. The apparatus of claim 13, in which the reference vector correcting means includes: multiplying means for multiplying the reference vector for the category by a first constant matrix to obtain a first product and for multiplying the writer-specific feature vector for the category by a second constant matrix to obtain a second product; and means for adding the first product to the second product to obtain the writer-specific reference vector for the category.