OFFSET
1,2
COMMENTS
Of course the total number of symmetric matrices of this type (not necessarily positive semi-definite) is 2^C(n,2).
This gives the number of different values of M + M' where M runs through the matrices counted in A038379. - Max Alekseyev, Nov 11 2006
EXAMPLE
The matrix
2 0 0 0 1
0 2 0 1 1
0 0 2 1 1
0 1 1 2 0
1 1 1 0 2
is one of the 100 5 X 5 matrices which are not positive semi-definite.
Its eigenvalues are approximately [2., -0.135779205069857, 4.135779205069857, 1.337846553138044, 2.662153446861956]
CROSSREFS
KEYWORD
nonn,more
AUTHOR
N. J. A. Sloane, Jul 12 2003
EXTENSIONS
3 more terms from Max Alekseyev, Nov 08 2006
STATUS
approved