Conference Matrices

Nickolay Balonin and

Jennifer SeberryTo Hadi

for your 70th birthday

Spot the Difference!

• Mathon C46 • Balonin-Seberry C46

In this presentation

• Two Circulant Matrices• Two Border Two Circulant Matrices• Two Border Four Circulant Matrices• Curl Resolution• Poor and Rich Structure Matrices• Multi-Circulant Conference Matrices• Sylvester Inspired Matrices• References

Definition

• The conference matrix C is n × n matrix 'С С=(n-1)I with zero diagonal and other ±1 units.

• The necessary condition for its existence: n-1 is sum of two squares.

• These orders don’t exist 22, 34, 58, 70, 78, 94, n<100.

• The known problem orders are 46 and 66

Two-Circulant Matrices

• Two circulant A,B-matrices are interesting due their universal structure: – they exist for complicated cases

10, 26, 50 (not for 46, 66, 86!), – A is circulant and symmetry, type

of matrix depends on circulant block B.

– Symmetric versions are equivalent to Paley constructions.

Two-circulant Examples

• C6 • C10

Matrices C14 and C18 Examples

Two-Circulant Matrix C82

Two Borders Two Circulant Matrices

• Two borders and two circulant A,B-matrices are interesting due to their universal structure: – they exist for prime power

plus 1 cases 10, 26, 50 (not for 46, 66, 86!),

– A is circulant and symmetric, – block B is based on the two

flip-inversed sequences

2 border and 2 circulant explained

• The 1st row and the 1st column are the same

• The 2nd row and 2nd column are the same

• Now the 4 circulants– take the form

A BB -A

2 Border 2 Circulant Examples

• C6 • C10

2 Border 2 Circulant Examples

• C18 • C30

2 Border 2 Circulant Examples

• C42 • C54

Two Borders Four Circulant Matrices

• Two borders and four A,B,C,D-cells core [S G;G' -S], S=[A B;B' A], G=[C D;F(-D) E(C)] we will call sequence of cells: A, B, C, D, E, F, situated as shown, the curl of Seberry.

• The solution depends on the curl resolution: it could be either poor or rich cell-construction.

• In comparison to the column separation of Walsh-matrices we see a kind of cell separation motivated by sign-frequency (look at C18) – This is a movement from mathematics to engineering concepts.

• C18

Curl Resolution

• A is circulant and symmetric matrix for the left top corner (excluding the two borders),

• the right square G=[C D;F C*] based on the two flip-inversed (or inversed or/and shifted) sequences for C and D,

• F=mirror(-D), E=C* may be shifted a few times (for orders 18, 26, 42, ..) the back-circulant cell is mirror(C).

• Matrix C38 with circulated entries

Curl Resolution

• A rich construction based on circulant and back circulant cells leads to matrix portraits with two curls. This form reflects a Fourier type basis for the orthogonal matrices (in some sense, these matrices reflect some gross-object given in fine detail when we consider big orders: something like the next example but with higher resolution).

Curl Resolution

• C62 Example

Matrices C26 – two versionsMatrix C26 is a special case; it has symmetry given by both diagonals of cell B (so it has a mirror symmetry of F=RDR or E=RCR, R is the back diagonal matrix) and it has a simple solution also.

C30 – Two Versions

C42 – Two Versions

Matrices of Poor and Rich Structure

• The solution depends on the curl resolution: • A is circulant and symmetric matrix in the top left corner

(excluding the two borders), • the right square G=[C D; D* C] is based on the two flip-

inversed (or shifted) sequences, • D* is a circulant cell shifted a few times. • The poor structures use only circulant matrices: rich

structures use circulant and back circulant matrices.• They look like block permutations of each other, but

column and row permutations of one cannot be equivalent to the other as the structure is not preserved.

Examples of Poor Matrices

• C42 • C50

Examples of Rich MatricesRich structures use circulant and back-circulant matrices

• C50• C42

Multi-circulant Conference Matrices

• C18 • Another C18

Multi-circulant Conference Matrix

• Main matrix consists of circulant blocks of circulant matrices.

• The set of symmetric A, D and some tied pair-sequences of (B, C) and (E, F), has enough invariants to describe conference matrices iff n–1 is prime.

Multi-circulant Conference Matrix

• This example shows the method with the pair-sequences, one sequence shifted to the left at (B, C) and to the right at (E, F).

• It could be any shift to any side, however they must be different.

• Example C30

Conference Matrices - Multiple Shifts

• Circulant Matrix C42 – 3 shifts

• Circulant Matrix C42– 4 shifts

Sylvester Method for Conference Matrices

• The Sylvester method, for orders n=2k+2 including matrices C6, C10, C18 has two borders and four blocks core [A B; B' -A'].

• order 34 does not exist • the next unsolved case is

order 66

• C18

Sylvester Method Examples

• C10 • C18

The Challenge of Order 66

• First try to find Max Det X66– Hadi Kharaghani

(following Young C.H., 1976) constructed a max det matrix of order 66 with 6x6 blocks of order 11 using Legendre symbols

• Maximal determinant matrix: det(X)=0.816*1060

References• N. A. Balonin and Jennifer Seberry, A Review and New Symmetric

Conference Matrices. Informatsionno-upravliaiushchie sistemy, 2014, no. 4 (71), 2--7

• V. Belevitch, Conference networks and Hadamard matrices, Ann. Soc. Sci. Brux. T. 82 (1968), 13-32.

• Christos Koukouvinos and Jennifer Seberry, New weighing matrices constructed using two sequences with zero autocorrelation function – a review, J. Stat. Planning and Inf., 81 (1999), 153-182

• R. Mathon. Symmetric conference matrices of order pq2+1 Canad. J. Math 30 (2), 321-331

• Jennifer Seberry, Albert L. Whiteman New Hadamard matrices and conference matrices obtained via Mathon's construction, Graphs and Combinatorics, 4, 1988, 355-377.

• Online: http://www.mathscinet.ru/catalogue/conference/

Thank YouHappy Birthday

Hadi

Kharahani's decomposition of K40 into 2 of the 4 Siamese SRG