311 research outputs found
The algebra of the box spline
In this paper we want to revisit results of Dahmen and Micchelli on
box-splines which we reinterpret and make more precise. We compare these ideas
with the work of Brion, Szenes, Vergne and others on polytopes and partition
functions.Comment: 69 page
Pure Differential Modules and a Result of Macaulay on Unmixed Polynomial Ideals
The first purpose of this paper is to point out a curious result announced by
Macaulay on the Hilbert function of a differential module in his famous book
The Algebraic Theory of Modular Systems published in 1916. Indeed, on page
78/79 of this book, Macaulay is saying the following: " A polynomial ideal
,..., is of the {\it
principal class} and thus {\it unmixed} if it has rank and is generated by
polynomials. Having in mind this definition, a primary ideal
with associated prime ideal is such that any
ideal of the principal class with determines a primary ideal of greater {\it multiplicity} over
. In particular, we have ,...,
because, passing to a system of PD equations for one unknown , the
parametric jets are \{\} but any ideal of
the principal class with is
contained into a {\it simple} ideal, that is a primary ideal
such that is a maximal and
thus prime ideal with at least.
Accordingly, any primary ideal may not be a member of the
primary decomposition of an unmixed ideal
of the principal class. Otherwise, is said to be of the {\it
principal noetherian class} ". Our aim is to explain this result in a modern
language and to illustrate it by providing a similar example for . The
importance of such an example is that it allows for the first time to exhibit
symbols which are -acyclic without being involutive. Another interest of
this example is that it has properties quite similar to the ones held by the
system of conformal Killing equations which are still not known. For this
reason, we have put all the examples at the end of the paper and each one is
presented in a rather independent way though a few among them are quite tricky.
Meanwhile, the second purpose is to prove that the methods developped by
Macaulay in order to study {\it unmixed polynomial ideals} are only particular
examples of new formal differential geometric techniques that have been
introduced recently in order to study {\it pure differential modules}. However
these procedures are based on the formal theory of systems of ordinary
differential (OD) or partial differential (PD) equations, in particular on a
systematic use of the Spencer operator, and are still not acknowledged by the
algebraic community
Macaulay inverse systems revisited
Since its original publication in 1916 under the title "The Algebraic Theory
of Modular Systems", the book by F. S. Macaulay has attracted a lot of
scientists with a view towards pure mathematics (D. Eisenbud,...) or
applications to control theory (U. Oberst,...).However, a carefull examination
of the quotations clearly shows that people have hardly been looking at the
last chapter dealing with the so-called "inverse systems", unless in very
particular situations. The purpose of this paper is to provide for the first
time the full explanation of this chapter within the framework of the formal
theory of systems of partial differential equations (Spencer operator on
sections, involution,...) and its algebraic counterpart now called "algebraic
analysis" (commutative and homological algebra, differential modules,...). Many
explicit examples are fully treated and hints are given towards the way to work
out computer algebra packages.Comment: From a lecture at the International Conference : Application of
Computer Algebra (ACA 2008) july 2008, RISC, LINZ, AUSTRI
Feynman integral relations from parametric annihilators
We study shift relations between Feynman integrals via the Mellin transform
through parametric annihilation operators. These contain the momentum space IBP
relations, which are well-known in the physics literature. Applying a result of
Loeser and Sabbah, we conclude that the number of master integrals is computed
by the Euler characteristic of the Lee-Pomeransky polynomial. We illustrate
techniques to compute this Euler characteristic in various examples and compare
it with numbers of master integrals obtained in previous works.Comment: v2: new section 3.1 added, several misprints corrected and additional
remark
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