z-form technique

The z-form technique is cited in several texts as a procedure for calculating a time series from the Laplace transform without factoring. Originally attributed to Boxer and Thaler [ibid., vol. 44, pp. 89-101, January 1965], it is cited by Thaler and Pastel [1962], J.E. Gibson [1963], and Horowitz [1963]. Horowitz bases his development on that of Wasow [1957]. Wasow´s presentation is more exact and convicing than that of Boxer and Thaler. There are some minor differences but both the Wasow and the Boxer-Thaler approximations areessentially the same. It is concluded that while Wasow as well as Boxer and Thaler may be right when the coefficients are exact, the approximation is highly sensitive to small errors and cannot be relied on to yield useful results.