1. Filtering to minimize some function of the errors. See ℓp fits, optimum filtering, and Sheriff and Geldart (1995, 298, 560). 2. For a waveform expressed as a z-transform, x(z), the value predicted after a delay of α sample intervals is zα A(z) x(z). The prediction error is [x(z)–zαx(z)] and the prediction error operator is [1–zαA(z)].