78×78 {-1, +1} matrix of largest known determinant

Ratio of |Det R| to Ehlich/Wojtas bound: 0.963616

M=R^TR= R R^T:

R:
The matrix has the form

 | X   J   K |
 |           |
 |  T        |
 | J   A   B |
 |           |
 |  T   T   T|
 | K   B  -A |

++
+-,

 ++++++...+
 ------...-,

The first rows of A and B are:
a, b:

-++-+++-+---++++-+--+++--+----+--+-++-
-+-+--++-+---+-+---+++---+----+-++++++

Notes:

1. Cannot achieve Ehlich/Wojtas bound since 77=78-1 is not the sum of two squares.
2. This form has not been proved to be optimal.
3. This determinant was discovered by Tomas Rokicki in April 2005 following Lars Backstrom's programming contest; it surpasses an old record.