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
- Pierre Massé (1962). Optimal Investment Decisions: Rules for Action and Criteria for Choice. Prentice-Hall. p. 142.
- James E. Gentle (2007). Matrix Algebra: Theory, Computations, and Applications in Statistics. Springer-Verlag. p. 42. ISBN 0-387-70872-3.
- 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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