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Lehmer matrix

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In mathematics, particularly matrix theory, the n×n Lehmer matrix (named after Derrick Henry Lehmer) is the constant symmetric matrix defined by

Alternatively, this may be written as

Properties

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As can be seen in the examples section, if A is an n×n Lehmer matrix and B is an m×m Lehmer matrix, then A is a submatrix of B whenever m>n. The values of elements diminish toward zero away from the diagonal, where all elements have value 1.

The inverse of a Lehmer matrix is a tridiagonal matrix, where the superdiagonal and subdiagonal have strictly negative entries. Consider again the n×n A and m×m B Lehmer matrices, where m>n. A rather peculiar property of their inverses is that A−1 is nearly a submatrix of B−1, except for the A−1n,n element, which is not equal to B−1n,n.

A Lehmer matrix of order n has trace n.

Examples

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The 2×2, 3×3 and 4×4 Lehmer matrices and their inverses are shown below.

See also

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References

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  • Newman, M.; Todd, J. (1958). "The evaluation of matrix inversion programs". Journal of the Society for Industrial and Applied Mathematics. 6 (4): 466–476. JSTOR 2098717.