Section:
New Results
Quasi-optimal computation of the
-curvature
The -curvature of a system of linear differential equations in positive
characteristic is a matrix that measures to what extent the system is
close to having a fundamental matrix of rational function solutions. This
notion, originally introduced in the arithmetic theory of differential
equations, has been recently used as an effective tool in computer algebra and
in combinatorial applications. We have described in [6]
a recent algorithm for computing the -curvature, whose complexity is almost
optimal with respect to the size of the output. The new algorithm performs
remarkably well in practice. Its design relies on the existence of a
well-suited ring, of so-called Hurwitz series, for which an analogue of the
Cauchy–Lipschitz Theorem holds, and on a FFT-like method in which the
“evaluation points” are Hurwitz series.