45,163 research outputs found
Explicit computations of Hida families via overconvergent modular symbols
In [Pollack-Stevens 2011], efficient algorithms are given to compute with
overconvergent modular symbols. These algorithms then allow for the fast
computation of -adic -functions and have further been applied to compute
rational points on elliptic curves (e.g. [Darmon-Pollack 2006, Trifkovi\'c
2006]). In this paper, we generalize these algorithms to the case of families
of overconvergent modular symbols. As a consequence, we can compute -adic
families of Hecke-eigenvalues, two-variable -adic -functions,
-invariants, as well as the shape and structure of ordinary Hida-Hecke
algebras.Comment: 51 pages. To appear in Research in Number Theory. This version has
added some comments and clarifications, a new example, and further
explanations of the previous example
The Construction of Finite Difference Approximations to Ordinary Differential Equations
Finite difference approximations of the form Σ^(si)_(i=-rj)d_(j,i)u_(j+i)=Σ^(mj)_(i=1) e_(j,if)(z_(j,i)) for the numerical solution of linear nth order ordinary differential equations are analyzed. The order of these approximations is shown to be at least r_j + s_j + m_j - n, and higher for certain special choices of the points Z_(j,i). Similar approximations to initial or boundary conditions are also considered and the stability of the resulting schemes is investigated
Numerical Solution of ODEs and the Columbus' Egg: Three Simple Ideas for Three Difficult Problems
On computers, discrete problems are solved instead of continuous ones. One
must be sure that the solutions of the former problems, obtained in real time
(i.e., when the stepsize h is not infinitesimal) are good approximations of the
solutions of the latter ones. However, since the discrete world is much richer
than the continuous one (the latter being a limit case of the former), the
classical definitions and techniques, devised to analyze the behaviors of
continuous problems, are often insufficient to handle the discrete case, and
new specific tools are needed. Often, the insistence in following a path
already traced in the continuous setting, has caused waste of time and efforts,
whereas new specific tools have solved the problems both more easily and
elegantly. In this paper we survey three of the main difficulties encountered
in the numerical solutions of ODEs, along with the novel solutions proposed.Comment: 25 pages, 4 figures (typos fixed
Algorithms yield upper bounds in differential algebra
Consider an algorithm computing in a differential field with several
commuting derivations such that the only operations it performs with the
elements of the field are arithmetic operations, differentiation, and zero
testing. We show that, if the algorithm is guaranteed to terminate on every
input, then there is a computable upper bound for the size of the output of the
algorithm in terms of the input. We also generalize this to algorithms working
with models of good enough theories (including for example, difference fields).
We then apply this to differential algebraic geometry to show that there
exists a computable uniform upper bound for the number of components of any
variety defined by a system of polynomial PDEs. We then use this bound to show
the existence of a computable uniform upper bound for the elimination problem
in systems of polynomial PDEs with delays
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