© 1979 by Oxford University Press
UNIFORM APPROXIMATIONS TO SOLUTIONS OF A LINEAR SECOND-ORDER DIFFERENTIAL EQUATION OUTSIDE A VANISHINGLY SMALL REGION CONTAINING TWO ASYMPTOTICALLY COINCIDENT TRANSITION POINTS
( Department of Engineering Mathematics, University of Newcastle upon Tyne )
Approximate solutions of the differential equation
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where v is a complex constant and
(
) = o(
) as
, are obtained for large |
|. The solutions are uniformly valid for any arg z and arg
, outside a vanishingly small neighbourhood of the origin, which contains the singularity
(
). Error estimates for both the solution and its derivative are given.
The comparison-equation method is used, the comparison equation being found by setting
= 0 in the given equation. A new feature in the application of this method is a representation of the modified Bessel functions, closely allied to their asymptotic expansions, which allows bounds to be placed on the functions for any order and argument.
