释义 |
Block DesignAn incidence system ( , , , , ) in which a set of points is partitioned into a family of subsets (blocks) in such a way that any two points determine blocks with points in each block, andeach point is contained in different blocks. It is also generally required that , which is where the``incomplete'' comes from in the formal term most often encountered for block designs, Balanced Incomplete BlockDesigns (BIBD). The five parameters are not independent, but satisfy the two relations
 | (1) |
 | (2) |
A BIBD is therefore commonly written as simply ( , , ), since and are given in terms of , , and by
A BIBD is called Symmetric if (or, equivalently, ).
Writing and , then the Incidence Matrix of the BIBD is given by the Matrix defined by
 | (5) |
This matrix satisfies the equation
 | (6) |
where is a Identity Matrix and is a matrix of 1s (Dinitz and Stinson 1992).
Examples of BIBDs are given in the following table. Block Design | ( , , ) | Affine Plane | ( , , 1) | Fano Plane | (7, 3, 1)) | Hadamard Design | Symmetric ( , , ) | Projective Plane | Symmetric ( , , 1) | Steiner Triple System | ( , 3, 1) | Unital | ( , , 1) |
See also Affine Plane, Design, Fano Plane, Hadamard Design, Parallel Class, ProjectivePlane, Resolution, Resolvable, Steiner Triple System, Symmetric Block Design, Unital References
Dinitz, J. H. and Stinson, D. R. ``A Brief Introduction to Design Theory.'' Ch. 1 in Contemporary Design Theory: A Collection of Surveys (Ed. J. H. Dinitz and D. R. Stinson). New York: Wiley, pp. 1-12, 1992. Ryser, H. J. ``The -Configuration.'' §8.1 in Combinatorial Mathematics. Buffalo, NY: Math. Assoc. Amer., pp. 96-102, 1963.
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