The Factorizational Theory of Finite Asymptotic Expansions in the Real Domain: A Survey of the Main Results
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ABSTRACT
<span
"="">After studying finite asymptotic expansions in real powers, we
have developed a general theory for expansions of type (*)
,x → x0<span "=""><span "=""> where the ordered n-tuple
forms an asymptotic scale at x0 <span "="">, i.e.
<span "=""> as x → x0, 1 ≤ i ≤ n – 1, and is practically assumed to be an extended complete Chebyshev system on a one-sided neighborhood of x o.
As in previous papers by the author concerning polynomial, real-power
and two-term theory, the locution “factorizational theory” refers to the
special approach based on various types of factorizations of a
differential operator associated to
<span "="">. Moreover, the <span "="">guiding thread of our
theory is the property of formal differentiation and we aim at
characterizing some n-tuples of asymptotic expansions formed by (*)<span "=""> <span "="">and n -1
expansions obtained by formal applications of suitable linear
differential operators of orders 1,2,…,n-1. Some considerations lead to
restrict the attention to two sets of operators naturally associated to
“canonical factorizations”. This gives rise to conjectures whose proofs
build an analytic theory of finite asymptotic expansions in the real
domain which, though not elementary, parallels the familiar results
about Taylor’s formula. One of the results states that to each scale of
the type under consideration it remains associated an important class of
functions (namely that of generalized convex functions) enjoying the
property that the expansion(*), if valid, is automatically formally
differentiable n-1 times in two special senses.
KEYWORDS
Asymptotic Expansions, Formal Differentiation of Asymptotic Expansions, Factorizations of Ordinary Differential Operators, Chebyshev Asymptotic Scales
Cite this paper
References
Granata, A. (2015) The Factorizational Theory of Finite Asymptotic Expansions in the Real Domain: A Survey of the Main Results. Advances in Pure Mathematics, 5, 1-20. doi: 10.4236/apm.2015.51001.
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