cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

Showing 1-3 of 3 results.

A158863 Maximal excess of a 3-normalized Hadamard matrix of order 4n.

Original entry on oeis.org

4, 8, 36, 32, 76, 72, 124, 128, 180, 200, 244, 288, 316
Offset: 1

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Author

William P. Orrick, Mar 28 2009

Keywords

Comments

The excess of a {-1,1} matrix is the sum of its elements. A Hadamard matrix is 3-normalized if its first three rows contain an even number of entries -1 in each column. 3-normalized Hadamard matrices of order 4n with large excess can be used to construct large-determinant {-1,1} matrices of order 4n+1.

Crossrefs

Cf. A004118.

A158865 Smallest maximal excess attained by an equivalence class of Hadamard matrices of order 4n.

Original entry on oeis.org

0, 8, 20, 36, 56, 80, 108, 140
Offset: 0

Views

Author

William P. Orrick, Mar 28 2009

Keywords

Comments

The excess of a {-1,1} matrix is the sum of its elements. The maximal excess of an equivalence class of Hadamard matrices (cf. A007299) is the largest excess attained by a member of the class. The largest maximal excess of any equivalence class is given by A004118.

Examples

			All equivalence classes in orders 20 and 28 attain the same maximal excess. In order 16, three classes attain maximal excess 64 and two attain maximal excess 56. In order 24, 56 equivalence classes attain maximal excess 112 and four attain maximal excess 108.
		

References

  • Best, M. R. The excess of a Hadamard matrix. Nederl. Akad. Wetensch. Proc. Ser. A {80}=Indag. Math. 39 (1977), no. 5, 357-361.
  • Brown, Thomas A. and Spencer, Joel H., Minimization of +-1 matrices under line shifts. Colloq. Math. 23 (1971), 165-171, 177 (errata).
  • R. Craigen and H. Kharaghani, Weaving Hadamard matrices with maximum excess and classes with small excess. J. Combinatorial Designs 12 (2004), 233-255.

Formula

For bounds on a(n), see A004118.

A210206 Maximal number of 1s in a Hadamard matrix of order 4n.

Original entry on oeis.org

12, 42, 90, 160, 240, 344, 462, 598, 756, 922, 1108, 1314, 1534, 1772
Offset: 1

Views

Author

N. J. A. Sloane, Mar 18 2012

Keywords

Comments

The weight of a {-1,1} matrix is defined to be the number of elements equal to 1. The excess is defined to be the sum of the matrix elements. The weight and excess of an N x N matrix are related by (weight) = (excess + N^2) / 2. Hence a(n) = (A004118+16n^2)/2. - William P. Orrick, Jun 25 2015

Crossrefs

Cf. A004118.

Extensions

a(5)-a(14) from William P. Orrick, Jun 25 2015
Farmakis & Kounias references added by William P. Orrick, Jun 25 2015
Showing 1-3 of 3 results.