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Overlooked degree of freedom in steepest descent method - steepest descent method corresponding to divergence-free WKB method. (English) Zbl 1196.41021

In previous papers, the authors have designed a divergence-free WKB asymptotic method for differential equations that yields a WKB approximation of the solution of that differential equation free from divergence for any real value of the asymptotic variable, even around the classical turning point. In this paper the authors claim that any WKB method for differential equations can be translated in one-to-one manner to the corresponding steepest descent method for integrals. In fact, in this paper the authors present a steepest descent method that corresponds to the above mentioned divergence-free WKB method previously designed by the authors. From this one-to-one translation, the authors notice that the key to convert the traditional steepest descent method for integrals into a divergence-free method is the choice of integration variable in the integral.

MSC:

41A60 Asymptotic approximations, asymptotic expansions (steepest descent, etc.)
41A58 Series expansions (e.g., Taylor, Lidstone series, but not Fourier series)
33C65 Appell, Horn and Lauricella functions
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