# Rank over Finite Fields and Codes

• Peter Bürgisser
• Michael Clausen
Part of the Grundlehren der mathematischen Wissenschaften book series (GL, volume 315)

## Abstract

Although the bilinear complexity of a bilinear map ϕ over a finite field may not be the minimum number of multiplications and divisions necessary for computing ϕ, the study of such maps gives some insight into the problem of computing a bilinear map over the ring of integers of a global field, such as the ring Z of integers: any bilinear computation defined over Z (that is, whose coefficients belong to Z) gives via reduction of constants modulo a prime p a bilinear computation over the finite field F p . In this chapter we introduce a relationship observed by Brockett and Dobkin [80] between the rank of bilinear maps over a finite field and the theory of linear error-correcting codes. More precisely, we associate to any bilinear computation of length r of a bilinear map over a finite field a linear code of block length r; the dimension and minimum distance of this code depend only on the bilinear map and not on the specific computation. The question about lower bounds for r can then be stated as the question about the minimum block length of a linear code of given dimension and minimum distance. This question has been extensively studied by coding theorists; we use their results to obtain linear lower bounds for different problems, such as polynomial and matrix multiplication. In particular, following Bshouty [85, 86] we show that the rank of n x n-matrix multiplication over F2 is 5/2n2o(n2). In the last section of this chapter we discuss an interpolation algorithm on algebraic curves due to Chudnovsky and Chudnovsky [110]. Combined with a result on algebraic curves with many rational points over finite fields, this algorithm yields a linear upper bound for R(F q n/F q )for fixed q.

## Keywords

Finite Field Linear Code Prime Power Prime Divisor Block Length
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

## Authors and Affiliations

• Peter Bürgisser
• 1
• Michael Clausen
• 2