Stability of linear predictive descriptions of curves used in handwriting

The technique of signal analysis by adaptive predictive filtering has previously been extended to the case of multidimensional signals, and it has been conjectured that this might be used to analyse handwriting as a cycloidal curve which is modulated to form the letter shapes. Although a second-order two-dimensional filter can model cycloids, the analysis procedure becomes unstable, and it is shown how differencing the input and applying a first-order filter rectifies this problem.