Hollow matrix

In mathematics, a hollow matrix may refer to one of several related classes of matrix.

Definitions

Sparse

A hollow matrix may be one with "few" non-zero entries: that is, a sparse matrix.[1]

Diagonal entries all zero

A hollow matrix may be a square matrix whose diagonal elements are all equal to zero.[2] The most obvious example is the real skew-symmetric matrix. Other examples are the adjacency matrix of a finite simple graph; a distance matrix or Euclidean distance matrix.

If A is an n×n hollow matrix, then the elements of A are given by

In other words, any square matrix that takes the form

is a hollow matrix.

For example:

is a hollow matrix.

Properties

  • The trace of A is zero.
  • If A represents a linear operator with respect to a fixed basis, then it maps each basis vector e into the complement of the span of e, i.e. where
  • Gershgorin circle theorem shows that the moduli of the eigenvalues of A are less or equal to the sum of the moduli of the non-diagonal row entries.

Block of zeroes

A hollow matrix may be a square n×n matrix with an r×s block of zeroes where r+s>n.[3]

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References

  1. Pierre Massé (1962). Optimal Investment Decisions: Rules for Action and Criteria for Choice. Prentice-Hall. p. 142.
  2. James E. Gentle (2007). Matrix Algebra: Theory, Computations, and Applications in Statistics. Springer-Verlag. p. 42. ISBN 0-387-70872-3.
  3. Paul Cohn (2006). Free Ideal Rings and Localization in General Rings. Cambridge University Press. p. 430. ISBN 0-521-85337-0.


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