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Heteroscedastic data

Consider a data set in which each data point tn is associated with a weighting factor rn > 0, so that the sum-of-squares error function becomes ED(w) = 1 2 X N n=1 rn  tn − w Tφ(xn) 2 . Find an expression for the solution w∗ that minimizes this error function. Give two alternative interpretations of the weighted sum-of-squares error function in terms of (i) data dependent noise variance and (ii) replicated data points. Can you see a situation where this model is usable?

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