Question
(a) A consumer organization wishes to test 12 different new perfumes, and has devised a number of tests to accomplish this. These tests are subject the following constraints:
• only six perfumes are to be tested by each tester;
• each pair of perfumes is to be compared the same number of times.
(i) Explain how a block design can be used to set up this experiment.
(ii) Find the set of parameters (v, b, k, r, λ) of such a design where the number of testers is as small as possible. List one other appropriate set of parameters for such a design.
(iii) Use a construction (from those described in Design 4) to construct such a design for which the number of testers is as small as possible.
(b) Let Δ be a BIBD with k = 5 and λ = 2. Explain why the number of varieties in Δ must have either the form 10n + 1 or the form 10n + 5, for some integer n.
(c) (i) Is the design that you constructed in part (a)(iii) resolvable?
(ii) Is a design as in part (b) with v = 21 resolvable?
Explain your answers briefly.
(d) Let Δ be a BIBD, let Δ_ be its complement, and let C and C_ be the codes whose codcwords are the rows of the incidence matrices of Δ and Δ_, respectively.
Show that the codes C and C- have the same Hamming distance.