Mathématiques de l'algèbre et de l'analyse computationels
Org: Keith Geddes, Mark Giesbrecht, George Labahn et Arne Storjohann (Waterloo)
- JACQUES CARETTE, McMaster University, Hamilton, Canada
Functors, CPS and monads, or how to generate efficient
algebraic code from abstract designs
Using monads and Ocaml's advanced module system in a generative
context, it is possible to totally eliminate the overhead of
abstraction. This lets one use extreme forms of information
hiding at no run-time cost. Furthermore the typed nature of the
generative context provide static guarantees about the generated code.
The various aspects of the algorithms can be made completely
orthogonal and compositional, even in the presence of name-generation
for temporaries and other bindings as well as "interleaving" of
aspects. We also show how to encode some domain-specific knowledge so
that "clearly wrong" compositions can be statically rejected by the
compiler. All our examples are drawn from numerical and symbolic
linear algebra (Gaussian Elimination, LU Decomposition,
Joint work with Oleg Kiselyov.
- FRED CHAPMAN, Waterloo
Hybrid Symbolic-Numeric Integration in Multiple Dimensions
via Tensor Product Series
We present a new hybrid symbolic-numeric method for the fast and
accurate evaluation of definite integrals in multiple dimensions.
This method is well-suited for two classes of problems:
(1) analytic integrands over general regions in two
(2) families of analytic integrands with special algebraic
structure over hyperrectangular regions in higher dimensions.
The algebraic theory of multivariate interpolation via natural tensor
product series was developed in the doctoral thesis by Chapman, who
named this broad new scheme of bilinear series expansions "Geddes
series" in honour of his thesis supervisor. This talk describes an
efficient adaptive algorithm for generating bilinear series of
Geddes-Newton type and explores applications of this algorithm to
multiple integration. We will present test results demonstrating that
our new adaptive integration algorithm is effective both in high
dimensions and with high accuracy. For example, Carvajal's Maple
implementation of our algorithm has successfully computed nontrivial
integrals with hundreds of dimensions to 10-digit accuracy, each in
under 3 minutes on a desktop computer.
Current numerical multiple integration methods either become very slow
or yield only low accuracy in high dimensions, due to the necessity to
sample the integrand at a very large number of points. Our approach
overcomes this difficulty by using a Geddes-Newton series with a
modest number of terms to construct an accurate tensor-product
approximation of the integrand. The partial separation of variables
achieved in this way reduces the original integral to a manageable
bilinear combination of integrals of essentially half the original
dimension. We continue halving the dimensions recursively until
obtaining one-dimensional integrals, which are then computed by
standard numeric or symbolic techniques.
This talk presents joint research with Orlando Carvajal and Keith
- JÜRGEN GERHARD, Maplesoft Inc., Waterloo, Ontario
Recent developments in rational summation
The talk discusses recent algorithmic developments for the problem of
rational summation: Given a univariate rational function g(x),
determine whether there exists a rational antidifference f(x), such
that f(x+1)-f(x)=g(x), and the more general problem of extracting a
maximal rationally summable part from g(x). The emphasis is on
improving the efficiency of rational summation algorithms. The
techniques used are modular methods and shiftless decomposition:
Modular methods lead to faster algorithms for all inputs. Shiftless
decomposition reduces the number of worst case inputs with exponential
running time behaviour.
This is joint work with Mark Giesbrecht, Arne Storjohann, and Eugene
- PASCAL GIORGI, Laboratoire LIP, ENSL, Lyon, France, and Waterloo
On the use of polynomial matrix approximant in the block
The resolution of a linear system is one of the most studied problems
in linear algebra. It is well known that by using Gaussian elimination
one can solve a linear system with a cubic time complexity. However,
when the matrix is sparse (only a few elements are non-zero) or
structured (Toeplitz, ...) the use of iterative methods such as
Krylov/Lanczos allows better time and space complexity. Nevertheless,
these methods are probabilistic and the chances of success rely on
randomness properties of the computation domain. In order to achieve
better probability of success one can use blocking technique. One of
the main concern in the Wiedemann algorithm is to compute the minimal
generating polynomial of matrix. When we switch to the block
Wiedemann algorithm the main concern becomes the computation of a
matrix minimal generating polynomial. The use of the block Wiedemann
algorithm leads us to deal with matrix polynomial operations instead
of scalar polynomial operations.
In order to provide fast computation in the block Wiedemann algorithm,
we use some recent reduction to matrix multiplication in polynomial
matrix computation. In particular, we rely on polynomial matrix
approximant (Pade Approximant) through minimal basis computation in
order to obtain the block minimal polynomial of a matrix. In
practice, the minimal basis allows us to use matrix multiplication and
so to benefit from implementation based on hybrid numerical/symbolic
computation. We present our work on the reduction of minimal basis
computation to matrix multiplication and we present an adaptation of
our algorithm to handle the computation of block minimal polynomial.
We also shows some performances obtained within the Linbox library
for the block Wiedemann algorithm using minimal
- ILIAS KOTSIREAS, Wilfred Laurier University
Astronomical Bounds for finding inequivalent Hadamard Matrices
Hadamard matrices arise in Combinatorics and have a wide range of
applications in Statistics, Coding Theory, Cryptography,
Telecommunications and many other areas. For each permissible order
(a multiple of 4) of Hadamard matrices there is only a finite number
of Hadamard matrices of this order. The set of Hadamard matrices of a
specific order is equipped with an equivalence relation and the
representatives of the equivalence classes with respect to this
relation are called inequivalent Hadamard matrices. The graph
isomorphism criterion is a necessary and sufficient condition to test
whether two given Hadamard matrices are inequivalent. The 4-profile
criterion is a necessary, but not sufficient, condition to test
whether two given Hadamard matrices are inequivalent. Both the graph
isomorphism and the 4-profile criteria have been implemented in the
Computer Algebra System Magma.
Using these and other criteria, various authors have established
constructive lower bounds (of the order of a few hundreds) for the
number of inequivalent matrices of many permissible orders. In this
work we use the doubling construction for Hadamard matrices, in
conjunction with the symmetric group (group of permutations) Sn, to
construct millions on inequivalent Hadamard matrices of orders which
are multiples of 8. Thus we establish constructively new lower bounds
for many such orders, up to 100, by starting with some small initial
sets of inequivalent, or equivalent, Hadamard matrices.
Joint work with G. Georgiou and C. Koukouvinos.
- JOHN MAY, North Carolina State University
Solving Problems in Approximate Polynomial Algebra via SVD
Many problems in polynomial algebra can be formulated for polynomials
which are given with inexact coefficients. When considered
numerically many of these algebraic problems are ill-posed-small
perturbations to coefficients lead to large changes in the answer.
For example, very small random changes to a factorizatable
multivariate polynomial typically result in an irreducible
polynomial. Other examples of problems of this type are polynomial
division, GCD computation and polynomial decomposition.
It is possible to find reasonable partial solutions for a number of
problems in approximate algebra by linearizing and using singular
value decomposition (SVD) methods. If the problem can be restated as
a problem of computing null vectors of a given matrix, then we
typically can do two things: first, given a polynomial without a given
property, we can find a lower bound on the distance to the nearest
polynomial with the property and second, we can compute a "nearby"
polynomial which has the given property, though we cannot in general
find the nearest such polynomial.
In this talk we will discuss the general technique, as well as the
specific details for the GCD, and factorization problems.
- MARC MORENO MAZA, University of Western Ontario
Equiprojectable decomposition of zero-dimensional varieties
Equidimensional decompositions of algebraic varieties, such as
triangular decompositions, are used for many situations. However,
even a zero-dimensional variety V may have several triangular
decompositions. The a priori canonical choice, namely the
irreducible decomposition of V, does not have good specialization
Given a variable ordering, we introduce the equiprojectable
decomposition of V. This is a canonical equidimensional
decomposition of V with good computational properties. We show how
to compute the equiprojectable decomposition of V from any triangular
decomposition or primitive element representation of V.
Given a zero-dimensional polynomial system F over Q, we show that
there exists an integer A whose height is softly in the order of the
square of the Bezout number of F, such that any prime number not
dividing A is a good prime for specializing the equiprojectable
decomposition of F.
Using Hensel lifting techniques, we deduce a modular algorithm for
computing the equiprojectable decomposition of zero-dimensional
varieties over Q. We have realized a preliminary implementation
with the Triade library developed in Maple by F. Lemaire. Our
theoretical results are comforted by these experiments.
Joint work with Xavier Dahan, Eric Schost, Wenyuan Wu and Yuzhen Xie.
- THOMAS WOLF, Brock University, Ontario
Partial and complete linearization of PDEs based on
In the talk a method is described that, based on infinite parameter
conservation laws, factors linear differential operators out of
nonlinear partial differential equations (PDEs) or out of differential
consequences of nonlinear PDEs. This includes a complete
linearization to an equivalent linear PDE (-system) if that is
possible. Comments are made concerning the computation of infinite
parameter conservation with the computer algebra package ConLaw.
- YANG ZHANG, Brandon University
Computing Valuation Popov Forms
Popov forms and weak Popov forms of matrices over noncommutative
valuation domains are defined and discussed. Two new algorithms to
construct these Popov forms are given, along with a description of
some of their applications.
This is joint work with Mark Giesbrecht and George Labahn.