50,937 research outputs found
Effective descent for differential operators
A theorem of N. Katz \cite{Ka} p.45, states that an irreducible differential
operator over a suitable differential field , which has an isotypical
decomposition over the algebraic closure of , is a tensor product
of an absolutely irreducible operator over and an
irreducible operator over having a finite differential Galois group.
Using the existence of the tensor decomposition , an algorithm is
given in \cite{C-W}, which computes an absolutely irreducible factor of
over a finite extension of . Here, an algorithmic approach to finding
and is given, based on the knowledge of . This involves a subtle descent
problem for differential operators which can be solved for explicit
differential fields which are -fields.Comment: 21 page
A machine learning framework for data driven acceleration of computations of differential equations
We propose a machine learning framework to accelerate numerical computations
of time-dependent ODEs and PDEs. Our method is based on recasting
(generalizations of) existing numerical methods as artificial neural networks,
with a set of trainable parameters. These parameters are determined in an
offline training process by (approximately) minimizing suitable (possibly
non-convex) loss functions by (stochastic) gradient descent methods. The
proposed algorithm is designed to be always consistent with the underlying
differential equation. Numerical experiments involving both linear and
non-linear ODE and PDE model problems demonstrate a significant gain in
computational efficiency over standard numerical methods
Holonomic Gradient Descent and its Application to Fisher-Bingham Integral
We give a new algorithm to find local maximum and minimum of a holonomic
function and apply it for the Fisher-Bingham integral on the sphere ,
which is used in the directional statistics. The method utilizes the theory and
algorithms of holonomic systems.Comment: 23 pages, 1 figur
Exponential asymptotics and Stokes lines in a partial differential equation
A singularly perturbed linear partial differential equation motivated by the geometrical model for crystal growth is considered. A steepest descent analysis of the Fourier transform solution identifies asymptotic contributions from saddle points, end points and poles, and the Stokes lines across which these may be switched on and off. These results are then derived directly from the equation by optimally truncating the naïve perturbation expansion and smoothing the Stokes discontinuities. The analysis reveals two new types of Stokes switching: a higher-order Stokes line which is a Stokes line in the approximation of the late terms of the asymptotic series, and which switches on or off Stokes lines themselves; and a second-generation Stokes line, in which a subdominant exponential switched on at a primary Stokes line is itself responsible for switching on another smaller exponential. The ‘new’ Stokes lines discussed by Berk et al. (Berk et al. 1982 J. Math. Phys.23, 988–1002) are second-generation Stokes lines, while the ‘vanishing’ Stokes lines discussed by Aoki et al. (Aoki et al. 1998 In Microlocal analysis and complex Fourier analysis (ed. K. F. T. Kawai), pp. 165–176) are switched off by a higher-order Stokes line
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