65.57 LexiCode

LexiCode( n, d, F )

In this format, Lexicode returns a Lexicode with word length n, design distance d over F. The code is constructed using the Greedy algorithm on the lexicographically ordered list of all vectors of length n over F. Every time a vector is found that has a distance to the current code of at least d, it is added to the code. This results, obviously, in a code with minimum distance greater than or equal to d.

    gap> C := LexiCode( 4, 3, GF(5) );
    a (4,17,3..4)2..4 lexicode over GF(5) 

LexiCode( B, d, F )

When called in this format, LexiCode uses the basis B instead of the standard basis. B is a matrix of vectors over F. The code is constructed using the Greedy algorithm on the list of vectors spanned by B, ordered lexicographically with respect to B.

    gap> B := [ [Z(2)^0, 0*Z(2), 0*Z(2)], [Z(2)^0, Z(2)^0, 0*Z(2)] ];;
    gap> C := LexiCode( B, 2, GF(2) );
    a linear [3,1,2]1..2 lexicode over GF(2) 

Note that binary Lexicodes are always linear.

The function GreedyCode creates a Greedy code that is not restricted to a lexicographical order (see GreedyCode).

Previous Up Top Next
Index

GAP 3.4.4
April 1997