A Borel
transform method for locating singularities of Taylor and
Fourier series
Uriel Frisch (Observatoire de Nice)
Observatoire de Nice
Given a Taylor series with a
finite radius ofconvergence, its Borel transform defines an entire
function. A theorem of
P\'olya relates the large distance behavior of the Borel transform in
different directions to singularities of the original
function. With the help of the new asymptotic interpolation method of
van der Hoeven, we show that from the knowledge
of a large number of Taylor coefficients we can identify
precisely the location of such singularities, as well as their type
when they are isolated. There is no risk of getting artefacts with this
method, which also gives us access to some of the singularities
beyond the convergence disk. The method can also be applied to
Fourier series of analytic periodic functions and is here tested on
various instances constructed from solutions to the Burgers equation.
Large precision on scaling exponents (up to twenty
accurate digits) can be achieved. [based on the paper by W. Pauls and
U. Frisch nlin.CD/0609025 ]