2014

Fast Matrix Multiplication: Limitations of the Laser Method

Ambainis, Andris, Filmus, Yuval, Gall, François Le

Understand

Until a few years ago, the fastest known matrix multiplication algorithm, due to Coppersmith and Winograd (1990), ran in time $O(n^{2.3755})$.

  • Recently, a surge of activity by Stothers, Vassilevska-Williams, and Le Gall has led to an improved algorithm running in time $O(n^{2.3729})$.
  • These algorithms are obtained by analyzing higher and higher tensor powers of a certain identity of Coppersmith and Winograd.
  • We show that this exact approach cannot result in an algorithm with running time $O(n^{2.3725})$, and identify a wide class of variants of this approach which cannot result in an algorithm with running time $O(n^{2.3078})$; in particular, this approach cannot prove the conjecture that for every $\epsilon > 0$, two $n\times n$ matrices can be multiplied in time $O(n^{2+\epsilon})$.

Built on

  • Gaussian elimination is not optimal

    Volker Strassen · 1969

    Earlier work this paper cites.

  • Vermeidung von Divisionen [Avoiding divisions]

    Volker Strassen · 1973

    Earlier work this paper cites.

  • Partial and total matrix multiplication

    Arnold Schönhage · 1981

    Earlier work this paper cites.

  • Relative bilinear complexity and matrix multiplication

    Volker Strassen · 1987

    Earlier work this paper cites.

  • Matrix multiplication via arithmetic progressions

    Don Coppersmith and Shmuel Winograd · 1990

    Earlier work this paper cites.

  • Tensor rank is NP-complete

    Johan Håstad · 1990

    Earlier work this paper cites.

Similar

  • Algebraic Complexity Theory

    Peter Bürgisser, Michael Clausen, and M. Amin Shokrollahi · 1997

    Cited alongside, same era.

  • A group-theoretic approach to fast matrix multiplication

    Henry Cohn and Chris Umans · 2003

    Cited alongside, same era.

  • On the complexity of matrix product

    Ran Raz · 2003

    Cited alongside, same era.

  • Group-theoretic algorithms for matrix multiplication

    Henry Cohn, Robert Kleinberg, Balázs Szegedy, and Chris Umans · 2005

    Cited alongside, same era.

  • On the complexity of matrix multiplication

    Andrew James Stothers · 2010

    Cited alongside, same era.

Then

  • Breaking the Coppersmith–Winograd barrier

    Virginia Vassilevska-Williams · 2012

    Later among the works it cites.

  • Fast matrix multiplication using coherent configurations

    Henry Cohn and Chris Umans · 2013

    Later among the works it cites.

  • Improved bound for complexity of matrix multiplication

    Alexander Munro Davie and Andrew James Stothers · 2013

    Later among the works it cites.

  • Most tensor problems are NP-hard

    Christopher J. Hillar and Lek-Heng Lim · 2013

    Later among the works it cites.

  • Powers of tensors and fast matrix multiplication

    François Le Gall · 2014

    Closest in time.

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