11. A method as in claim 10 wherein the modified training portion produced by step (vii) of one iteration of steps (vi) to (ix) constitutes the training portion of step (vii) of the next iteration thereof.
16. A method as in claim 11, wherein the weight modifying function comprises multiplying each weight (Wi) by a respective weight factor (1+ki), where ki is a function of the contribution that the respective weighted comparison result makes to the dissimilarity measure, and the difference between the initial comparison result and the further comparison result.