1. A circuit for determining a best fit to input signals with a selected set of basis functions .epsilon..sub.k, which are signal functions of a preselected variable, said circuit comprising: an N plurality of gain-providing amplifiers, where N is a chosen number with each amplifier A.sub.i having an input terminal and output terminal; and conductance devices of conductance value T.sub.ij, with each conductance device connecting said output terminal of amplifier A.sub.i to the input terminal of amplifier A.sub.j, i and j being subscripts that denote a particular of said amplifiers and conductance devices wherein each of said conductance values T.sub.ij is related to the dot product of the i.sup.th basis function .epsilon..sub.i and the j.sup.th basis function .epsilon..sub.j.