Application of the Padé Approximant to Scattering Theory

The Padé approximant is shown to yield exactly unitary $S$ matrices in scattering theory. The method is used to construct a unitary $S$ matrix for $n-d$ scattering above the threshold for inelastic scattering. Thus the effect of inelastic scattering on elastic-scattering total cross sections and angular distributions is calculated. No cusps are found at the threshold.