DE>n2</CODE> of the squared
distances between centres and inputs, and a matrix <CODE>deltas</CODE> of the 
gradient of the error function with respect to the values of the
output units (i.e. the summed inputs to the output units, before the
activation function is applied). The return value is the gradient
<CODE>g</CODE> of the error function with respect to the network
weights. Each row of <CODE>x</CODE> corresponds to one input vector.

<p>This function is provided so that the common backpropagatio