The Lanczos Tau-method

A number of variants of the -method, giving polynomial and rationalapproximations, are examined by applying them to the initial-valueproblem y¹—y = 0, y(0) = 1 on the interval [0, 1]. Errorestimates are derived for the rational approximations. A rationalapproximation, obtained by using a multiple of the shifted Legendrepolynomial as the perturbing term, proves to be the most accurateof the approximations studied.     

Numerical Methods for y' =f(x, y) via Rational Approximations for the Cosine

To investigate stability and phase lag, a numerical method isapplied to the test equation y' = –²y. Frequently, thecharacteristic equation of the resulting recurrence relationhas the form ²– 2R_nm(v²) + 1 = 0, where v = h, with hthe steplength, and R_nm(v²) is a rational approximation forcos v. In this paper, properties of such approximations areused to provide a general framework for the study of stabilityintervals and orders of dispersion of a variety of one- andtwo-step methods. Upper bounds on the intervals of periodicityof explicit methods with maximum order of dispersion are established.It is shown that the order of dispersion of a P-stable method,for given n and m, cannot exceed 2m; a consequence is that,of the Pad? approximants for cos v, only the [0/2m] approximantshave modulus less than unity for all v² >0. A complete characterizationof P-stable methods of fourth order corresponding to the rationalapproximation R₂₂(v²) is followed by several results for methodswhich have finite intervals of periodicity; in particular, weidentify methods which have order of dispersion 6 or 8 withlarge intervals of periodicity. There is also a detailed discussionof P-stable methods of sixth order corresponding to the rationalapproximation R₃₃(v²).     

On Some Steady-state Moving Boundary Problems in the Linear Theory of Viscoelasticity

Three steady-state moving boundary problems in the linear theoryof viscoelasticity are considered when the inertia terms aretaken into account. Attention is directed to the dimensionlessparameter = V/L where V is the speed of the boundary, is therelaxation time of the medium, and L is a length associatedwith the geometry of the problem. When is small the problemsare recognized as having a singular perturbation character andthe method of matched asymptotic expansions is used. The problemsare (i) a semi-infinite crack moving steadily in a clamped viscoelasticstrip, (ii) a finite length crack moving in an infinite viscoelasticmedium, and (iii) a steady rolling cylinder on a visco-elastichalf-space.