OFFSET
1,5
COMMENTS
"A linear (n, k)-code has columns of zeros, if and only if there is some i ∈ n such that x_i = 0 for all codewords x, and so we should exclude such columns." [Fripertinger and Kerber (1995, p. 196)] - Petros Hadjicostas, Sep 30 2019
LINKS
Discrete algorithms at the University of Bayreuth, Symmetrica.
Harald Fripertinger, Isometry Classes of Codes.
Harald Fripertinger, Snk2: Number of the isometry classes of all binary (n,k)-codes without zero-columns. [This is a lower triangular array whose lower triangle contains T(n,k). In the papers, the notation S_{nk2} is used.]
H. Fripertinger and A. Kerber, Isometry classes of indecomposable linear codes. In: G. Cohen, M. Giusti, T. Mora (eds), Applied Algebra, Algebraic Algorithms and Error-Correcting Codes, 11th International Symposium, AAECC 1995, Lect. Notes Comp. Sci. 948 (1995), pp. 194-204. [Here S_{nk2} = T(n,k).]
Petros Hadjicostas, Generating function for column k = 4. [Cf. A034345.]
Petros Hadjicostas, Generating function for column k = 5. [Cf. A034346.]
Petros Hadjicostas, Generating function for column k = 6. [Cf. A034347.]
Petr Lisonek, Combinatorial families enumerated by quasi-polynomials, J. Combin. Theory Ser. A 114(4) (2007), 619-630. [See Section 5.]
David Slepian, Some further theory of group codes, Bell System Tech. J. 39(5) (1960), 1219-1252.
David Slepian, Some further theory of group codes, Bell System Tech. J. 39(5) (1960), 1219-1252.
Wikipedia, Cycle index.
Wikipedia, Projective linear group.
FORMULA
From Petros Hadjicostas, Sep 30 2019: (Start)
T(n,k=2) = floor(n/2) + floor((n^2 + 6)/12) = A253186(n).
G.f. for column k=2: (x^3 - x - 1)*x^2/((x^2 + x + 1)*(x + 1)*(x - 1)^3).
G.f. for column k=3: (x^12 - 2*x^11 + x^10 - x^9 - x^6 + x^4 - x - 1)*x^3/((x^6 + x^5 + x^4 + x^3 + x^2 + x + 1)*(x^2 + x + 1)^2*(x^2 + 1)*(x + 1)^2*(x - 1)^7).
G.f. for column k >= 4: modify the Sage program below (cf. function f). It is too complicated to write it here. See also some of the links above.
(End)
EXAMPLE
Triangle T(n,k) (with rows n >= 1 and columns k >= 1) begins as follows:
1;
1 1;
1 2 1;
1 3 3 1;
1 4 6 4 1;
1 6 12 11 5 1;
1, 7, 21, 27, 17, 6, 1;
1, 9, 34, 63, 54, 25, 7, 1;
1, 11, 54, 134, 163, 99, 35, 8, 1;
...
PROG
(Sage) # Fripertinger's method to find the g.f. of column k >= 2 (for small k):
def A034253col(k, length):
G1 = PSL(k, GF(2))
G2 = PSL(k-1, GF(2))
D1 = G1.cycle_index()
D2 = G2.cycle_index()
f1 = sum(i[1]*prod(1/(1-x^j) for j in i[0]) for i in D1)
f2 = sum(i[1]*prod(1/(1-x^j) for j in i[0]) for i in D2)
f = f1 - f2
return f.taylor(x, 0, length).list()
# For instance the Taylor expansion for column k = 4 gives
print(A034253col(4, 30)) # Petros Hadjicostas, Sep 30 2019
CROSSREFS
KEYWORD
tabl,nonn
AUTHOR
STATUS
approved