Optimal Ferrers Diagram Rank-Metric Codes

Optimal rank-metric codes in Ferrers diagrams are considered. Such codes consist of matrices having zeros at certain fixed positions and can be used to construct good codes in the projective space. First, we consider rank-metric anticodes and prove a code-anticode bound for Ferrers diagram rank-metric codes. The size of optimal linear anticodes is given. Four techniques and constructions of Ferrers diagram rank-metric codes are presented, each providing optimal codes for different diagrams and parameters for which no optimal solution was known before. The first construction uses maximum distance separable codes on the diagonals of the matrices, the second one takes a subcode of a maximum rank distance code, and the last two combine codes in small diagrams to a code in a larger diagram. The constructions are analyzed and compared, and unsolved diagrams are identified.