1. Artificial neural network classifier comprising: a plurality of stages including an input layer, an output layer and at least a hidden layer intermediate said input layer and said output layer, each node comprising a summer, a function system to operate on a sum produced at said node, the function circuit providing an operator of ( 2 ⁢ t j - 1 ) n - 1 ⁢ ( t j - y j L ) n y j L ⁡ ( 1 - y j L ) = ⅆ y j L , where t j is the value of an error signal at a node j, n is greater than or equal to two and L is the number of layers.