Computer Algebra and Computer Algebra Systems
Org: Michael Monagan (SFU) [PDF]
 OLEG GOLUBITSKY, Ontario Research Centre for Computer Algebra, London,
Ontario, Canada, N6A 5B7
Implementation of Arithmetics in Aldor
[PDF] 
ALDOR is a programming language designed for implementing
symbolic computation algorithms. On the one hand, it allows to encode
mathematical structures and algorithms in a natural way, exhibiting
their essence and hiding various lowerlevel programming issues. On
the other hand, the ALDOR compiler allows to use machine
resources much more efficiently than computer algebra systems.
The efficiency of implementation of most symbolic methods
significantly depends on the efficiency of basic arithmetic
operations. The latter include computations with fixed size integers,
residue classes modulo an integer, arbitrary precision integers,
single and double floating point numbers, and arbitrary precision
floating point numbers.
We will discuss a new implementation of arithmetic types in Aldor,
which combines and extends two existing ALDOR libraries,
AXLLIB and LIBALDOR. In this implementation, we
refine the hierarchy of arithmetic types in an attempt to reflect
structural relationships between them more naturally. We also solve
the issue of compatibility with multiple platforms, on which the
machine arithmetic types may have different sizes. In particular, we
develop a general framework for doubling the size of a given machine
integer type or restricting it to an integer of smaller size
(including a new algorithm for dividing double integers). We show how
the ALDOR optimizer translates this generic objectoriented
code into highly efficient machine code by inlining small subroutines
and unfolding records.
This work is part of a larger project on unifying existing
ALDOR libraries and providing one efficient generalpurpose
library for implementing computer algebra algorithms.
This is joint work with Stephen Watt.
 HOWARD CHENG, University of Lethbridge, 4401 University Drive, Lethbridge,
Alberta
Time and SpaceEfficient Evaluation of Some Hypergeometric
Constants
[PDF] 
The current best practical algorithms for the numerical evaluation
of hypergeometric constants such as z(3) to d decimal digits
have time complexity O ( M(d) log^{2} d ) and space
complexity of O(d logd) or O(d). Following work from Cheng,
Gergel, Kim and Zima, we present a new algorithm with the same
asymptotic complexity, but more efficient in practice. Our
implementation of this algorithm improves over existing programs for
the computation of p, and we announce a new record of 2 billion
digits for z(3).
This work was done jointly with Eugene Zima (Wilfrid Laurier
University), Guillaume Hanrot, Emmanuel Thomé, and Paul Zimmermann
(INRIA, France).
 VAHID DABBAGHIANABDOLY, Simon Fraser University, Burnaby, BC, V5A 1S6
Implementation of Cellular Automata Models on Maple
[PDF] 
Cellular Automata is a discrete dynamical model providing an excellent
platform for performing behaviour of complex systems with the help of
only local information. In this talk I will present a cellular
automata model for describing the dynamics of urban transformations
such as spread of infectious disease and crime. In particular I will
show implementation of some cellular automata models on Maple.
 RON FERGUSON, Simon Fraser University
Search Algorithms for Low Autocorrelation Sequences
[PDF] 
Low autocorrelation sequences have been studied both for their number
theoretic properties and for applications in communications
engineering. Such problems as the merit factor problem, the peak
sidelobe problem and the existence of barker sequences are both
computationally challenging and have deep theoretical implications.
The problems may be discrete, as in the cases of binary or nphase
sequences, or continuous, where the sequences are unimodular. We will
describe algorithms used to obtain computational results, combining
both continuous and discrete approaches as well as both exhaustive and
stochastic methods.
 MARK GIESBRECHT, University of Waterloo, School of Computing Science
Complexity and Practicality in Sparse Matrix Computation
[PDF] 
We present new algorithms for operations related to sparse matrices
which are asymptotically faster than those known previously and quite
practical in some cases. Sparsity is designated by requiring a fast
matrixvector producttypically quasilinear timewhich captures
many traditional families of sparse or structured matrices. We
exhibit a probabilistic algorithm which finds the (dense) inverse of
such a sparse matrix with O(n^{2.27}) field operations. This is
surprising in that it is less than the cost of dense matrix
multiplication and inversion, which was the previously best known
approach to sparse matrix inversion. For sparse integer matrices
(with constant sized entries), we show how to solve such systems with
O(n^{2.5}) machine operations using standard matrix arithmetic.
These techniques are shown to be practical at least on some classes of
large sparse matrices.
This is joint work with Wayne Eberly, Pascal Giorgi, Arne Storjohann
and Gilles Villard.
 OLEG GOLUBITSKY, University of Western Ontario
Comprehensive Triangular Decomposition
[PDF] 
We introduce the concept of comprehensive triangular decomposition
(CTD) for a parametric polynomial system F with coefficients in a
field. In broad words, this is a finite partition of the the
parameter space into regions, so that within each region the
"geometry" (number of irreducible components together with their
dimensions and degrees) of the algebraic variety of the specialized
system F(u) is the same for all values u of the parameters. We
propose an algorithm for computing the CTD of F. It relies on a
procedure for solving the following set theoretical instance of the
coprime actorization problem.
Given a family of constructible sets, A_{1},...,A_{s} compute a family
B_{1},...,B_{t} of pairwise disjoint constructible sets such that, for
all index i, the set A_{i} writes as a union of some of the
B_{1},...,B_{t}. We report on an implementation of our algorithm
computing CTDs, based on the RegularChains library in Maple. We
provide comparative benchmarks with Maple implementations of related
methods for solving parametric polynomial systems. Our results
illustrate the good performances of our CTD code.
This is joint work with Changbo Chen, Francois Lemaire, Marc Moreno
Maza and Wei Pan.
 BRYAN KRAWETZ, MapleSoft, 615 Kumpf Drive, Waterloo, Ontario
Faster polynomial arithmetic over algebraic number and
function fields in Maple 11
[PDF] 
In Maple, the command evala is used to evaluate expressions in
an algebraic number (or function) field. When conditions are
appropriate, evala relies on recden, a Maple library designed
to work with dense polynomials efficiently. The recden library was
developed by M. Monagan and his group at Simon Fraser University.
For Maple 11, the core routines of the recden library were converted
to internal kernel routines. In this talk, we will give an overview
of how these new routines are implemented, as well, we will discuss
the performance benefits they provide over the pure library
implementation.
 SCOTT MACLEAN, University of Waterloo
Mathematical Symbol Recognition in the MathBrush System
[PDF] 
The MathBrush project at the University of Waterloo is a vehicle for
investigating issues which arise in the construction of penbased
interfaces for computer algebra systems. Our prototype application
currently comprises several components including an interface module,
a prettyprinter, a symbol recognizer, and a structural analyzer.
Here, we outline the MathBrush system in its entirety but focus on the
symbol recognition module, demonstrating particular difficulties
associated with recognizing symbols in the context of mathematical
expressions as opposed to English text and describing our techniques
for addressing these difficulties. We detail our experiments with
various recognition algorithms, our approach to stroke grouping in a
mathematical context, and aspects of our recognizer intended to
improve performance and usability. Ongoing work incorporating
feedback between the symbol recognition and structural analysis
modules to improve recognition accuracy is also described.
 MATT MALENFANT, University of Western Ontario
Better Evaluation Points for the Interpolation of Sparse
Symbolic Polynomials
[PDF] 
Symbolic polynomials, whose exponents themselves are integervalued
multivariate polynomials, arise often in algorithm analysis.
Unfortunately, modern computer algebra systems do not provide ample
support for said algebraic structures. Basic operations involving
symbolic polynomials are indeed trivial (addition, multiplication,
derivatives); however, other crucial operations remain much more
difficult, such as factorization, GCD, Gröbner Bases.
The exponent variables can be evaluated, producing Laurent Polynomials
which can then be interpolated back to their original form. For a
tsparse exponent polynomials of p variables and degree d,
sparse interpolation can be used to reduce the required number of
images from O ( (d+1)^{p} ) to O(pdt).
In practice, selecting random, or small evaluations will often result
in polynomials of very large degree. In this talk, we will describe a
method of selecting evaluation points, that will minimize the maximum
degree of the input symbolic exponents.
 MICHAEL MONAGAN, University of Western Ontario
Solving Linear Systems over Cyclotomic Fields
[PDF] 
We present three algorithms for solving a linear system Ax = b over
a cyclotomic field. If m(z) is the minimal polynomial for the
field, a cyclotomic polynomial, then what makes this problem of
special interest is that it is relatively easy to find primes which
split m(z) into linear factors. This means we can solve Ax = b
modulo a prime at each root of m(z), potentially in parallel.
Our first algorithm uses Chinese remaindering and rational
reconstruction. Our second algorithm uses linear padic lifting and
rational reconstruction. A third approach is to express the solutions
as ratios of determinants. This can be a factor of d = degm(z)
more compact.
In the talk we will present the algorithms and improvements made to
improve the complexity of the reconstruction, and, for the padic
lifting approach, computation of the error.
We have implemented the three algorithms in Maple. We present timings
comparing the three algorithms on two sets of benchmarks, firstly, a
set of real problems arising from computational group theory. These
problems have the property that the size of the rationals in the
solution vector x is much smaller than they can be in general. The
second set is for problems where the integers in the input are
generated at uniformly at random.
This is joint work with Liang Chen at SFU.
 ROMAN PEARCE, Simon Fraser University
Sparse Polynomial Arithmetic using Heaps
[PDF] 
We present some old and seemingly forgotten algorithms for multiplying
and dividing sparse polynomials using heaps. The algorithms do an
nary merge of all partial products using only a heap of pointers
into the input, constructing exactly the terms that appear in the
result. The amount of memory required is linear in the size of the
smaller input for multiplication or in the quotient or the divisor for
division. We also constructed a variant of the division algorithm
that is linear time in the size of the quotient, something which is
not possible for algorithms based on merging. As a result, some
common cases of exact division can be done an order of magnitude
faster using an order of magnitude less memory than with a divide and
conquer strategy, such as geobuckets. We plan to integrate our
C library into the next release of Maple.
This is joint work with Dr. Michael Monagan at Simon Fraser
University.
 GREG REID, Department of Applied Mathematics, University of Western
Ontario, Middlesex College, London, ON, N6A 5B7
Introduction to SymbolicNumeric Completion Methods for PDE
[PDF] 
Differential elimination methods apply a finite sequence of
differentiations and eliminations to general systems of PDE to extract
potent information about their solutions. Much recent progress has
been made in the design and implementation of exact algorithms,
applying to exact input sytems, by researchers such as Boulier,
Hubert, Mansfied, Seiler, Wittkopf and others. Though powerful, such
methods cannot be applied to approximate systems, since the strong
underlying use of rankings of partial derivatives, often induces
instability, by forcing such methods to pivot on small quantities.
The talk will be an introduction to the new area of symbolicnumeric
methods for completion of PDE. Main features include the focus on
geometric methods and the use of homotopycontinuation methods for the
detection of new constraints by slicing varieties in jet space with
random hyperplanes. Our most recent work on this topic will be
presented in this talk.
 ALLAN WITTKOPF, MapleSoft, 615 Kumpf Drive, Waterloo, Ontario, N2V 1K8
What's new in Maple 11
[PDF] 
I will give an overview of the new features in Maple 11, including:
 interface features, such as drawing, and new array plots;
 new packages (Graph Theory, Physics, etc.);
 symbolic computation improvements (Groebner, summation,
inequality solving);
 numeric computation improvements (fsolve, numeric
integration/summation, ODE solutions);
and several other features.
 WENYUAN WU, Department of Applied Mathematics, University of Western
Ontario, Middlesex College, London, ON, N6A 5B7
New Progress on Implicit Riquier Bases for PDE
[PDF] 
Riquier Bases for systems of analytic PDE are, loosely speaking, a
differential analogue of Grobner Bases for polynomial equations. They
are determined in the exact case by applying a sequence of
prolongations and eliminations to an input system of PDE.
We present a symbolicnumeric method to determine Riquier Bases in
implicit form for systems which are dominated by pure derivatives in
one of the independent variables and have the same number of PDE and
unknowns. The method is successful provided the prolongations with
respect to the dominant independent variable have a block structure
which is uncovered by Linear Programming and certain Jacobians are
nonsingular when evaluated at points on the zero sets defined by the
functions of the PDE. For polynomially nonlinear PDE, homotopy
continuation methods from Numerical Algebraic Geometry can be used to
compute approximations of the points.
 WEI ZHOU, University of Waterloo
Fractionfree Computation of LCM and GCD by values
[PDF] 
Given the values of two univariate polynomials at a set of
interpolation points, we examine the problem of computing the values
of their least common multiple (LCM) and their greatest common divisor
(GCD) at these points. We show that the values of an LCM of two
univariate polynomials can be computed directly from the values of the
polynomials and the interpolation points without first converting the
polynomials to the standard power form. The result is the
interpolation data for the LCM of the input polynomials. The values
of a GCD can then be computed from the values of the LCM.
