Clément Pernet

Memory efficient scheduling of Strassen-Winograd's matrix multiplication algorithm

We propose several new schedules for Strassen-Winograds matrix multiplication algorithm, they reduce the extra memory allocation requirements by three different means: by introducing a few pre-additions, by overwriting the input matrices, or by using a first recursive level of classical multiplication. In particular, we show two fully in-place schedules: one having the same number of operations, if the input matrices can be overwritten; the other one, slightly increasing the constant of the leading term of the complexity, if the input matrices are read-only. Many of these schedules have been found by an implementation of an exhaustive search algorithm based on a pebble game.

LINBOX founding scope allocation, parallel building blocks, and separate compilation

As a building block for a wide range of applications, computational exact linear algebra has to conciliate efficiency and genericity. The goal of the LinBox project is to address this problem in the design of an efficient general-purpose C++ opensource library for exact linear algebra over the integers, the rationals, and finite fields. Matrices can be either dense, sparse or black box (i.e. viewed as a linear operator, acting on vectors only). The library proposes a set of high level linear algebra solutions, such as the rank, the determinant, the solution of a linear system, the Smith normal form, the echelon form, the characteristic polynomial, etc.

Output-sensitive decoding for redundant residue systems

We study algorithm based fault tolerance techniques for supporting malicious errors in distributed computations based on Chinese remainder theorem. The description holds for both computations with integers or with polynomials over a field. It unifies the approaches of redundant residue number systems and redundant polynomial systems through the Reed Solomon decoding algorithm proposed by Gao. We propose several variations on the application of the extended Euclid algorithm, where the error correction rate is adaptive. Several improvements are studied, including the use of various criterions for the termination of the Euclidean Algorithm, and an acceleration using the Half-GCD techniques. When there is some redundancy in the input, a gap in the quotient sequence is stated at the step matching the error correction, which enables early termination parallel computations. Experiments are shown to compare these approaches.

On finding multiplicities of characteristic polynomial factors of black-box matrices

We present algorithms and heuristics to compute the characteristic polynomial of a matrix given its minimal polynomial. The matrix is represented as a black-box, i.e., by a function to compute its matrix-vector product. The methods apply to matrices either over the integers or over a large enough finite field. Experiments show that these methods perform efficiently in practice. Combined in an adaptive strategy, these algorithms reach significant speedups in practice for some integer matrices arising in an application from graph theory.

Elements of Design for Containers and Solutions in the LinBox Library

We describe in this paper new design techniques used in the C++ exact linear algebra library LinBox, intended to make the library safer and easier to use, while keeping it generic and efficient. First, we review the new simplified structure for containers, based on our founding scope allocation model. We explain design choices and their impact on coding: unification of our matrix classes, clearer model for matrices and submatrices, etc. Then we present a variation of the strategy design pattern that is comprised of a controller–plugin system: the controller (solution) chooses among plug-ins (algorithms) that always call back the controllers for subtasks. We give examples using the solution mul. Finally we present a benchmark architecture that serves two purposes: Providing the user with easier ways to produce graphs; Creating a framework for automatically tuning the library and supporting regression testing.