The Expected Norm of Random Matrices

  • Authors:
  • Yoav Seginer

  • Affiliations:
  • Check Point Software Technologies Ltd., 3A Jabotinsky St., Diamond Tower, Ramat Gan, 52520, Israel (e-mail: yoav@checkpoint.com)

  • Venue:
  • Combinatorics, Probability and Computing
  • Year:
  • 2000

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Abstract

We compare the Euclidean operator norm of arandom matrix with the Euclidean norm of its rows and columns. Inthe first part of this paper, we show that if A is a randommatrix with i.i.d. zero mean entries, thenE∥A∥h ≤Kh (E maxi∥ai•∥h + E maxj∥aj•∥h), where K is a constant whichdoes not depend on the dimensions or distribution of A(h, however, does depend on the dimensions). In the secondpart we drop the assumption that the entries of A are i.i.d.We therefore consider the Euclidean operator norm of a randommatrix, A, obtained from a (non-random) matrix byrandomizing the signs of the matrix's entries. We show that in thiscase, the best inequality possible (up to a multiplicativeconstant) is E∥A∥h≤ (c log1/4 min {m,n})h (E maxi∥ai• ∥h+ E maxj∥aj•∥h) (m, n the dimensions ofthe matrix and c a constant independent of m,n).