====================================================================== SOURCE FILE: minimax_ex30_noshow_before.yaml TABULATED FILE: minimax_ex30_noshow_before_tabulated.txt ====================================================================== election_title: "Minimax Ex.30 — before: all 19 vote, Minimax elects B" scenario_description: |- The BEFORE half of Felsenthal's Minimax no-show pair. Source: Dan S. Felsenthal, "Review of Paradoxes Afflicting Various Voting Procedures Where One Out of m Candidates (m ≥ 2) Must Be Elected", University of Haifa / LSE, revised 26 May 2010; Appendix A10, Example 30 (credited to Hannu Nurmi, private communication 22.2.2010). 19 voters, four candidates: 5×(D>B>C>A), 4×(B>C>A>D), 3×(A>D>C>B), 3×(A>D>B>C), 4×(C>A>B>D). The social ordering cycles (C>A>D>B>C), so there is no Condorcet winner and Minimax must fall back on its second clause — elect whoever's worst pairwise loss is smallest. Worst losses: A 13, B 11, C 12, D 14, so Minimax elects B. Then compare minimax_ex30_noshow_after.yaml, where three of the four C>A>B>D voters stay home and A wins instead — an outcome those absent voters PREFER to B. That is the no-show paradox, and read in the other direction it is the twin paradox. Labels are Felsenthal's own A/B/C/D so the case can be read side by side with the paper's table; this is an academic reproduction, not a scenario with a cast. Minimax has no tabulator in the LH engine or on BetterVoting, so the file is tabulated here as Ranked Robin — which prints the full pairwise matrix, the exact object Minimax reads. Ranked Robin then breaks the Copeland tie by margin and elects A, not B: same matrix, different cycle-breaker. For the Minimax count itself run tools_adam/pref_voting_tabulation_engine/minimax_report.py, which is cross-checked against pref_voting. paradoxes: [no-show, twin, condorcet-cycle] voting_method: RankedRobin num_winners: 1 ballots: |- 5:D>B>C>A 4:B>C>A>D 3:A>D>C>B 3:A>D>B>C 4:C>A>B>D expected_winners: - A # file: minimax_ex30_noshow_before.yaml ====================================================================== TABULATION RESULTS ====================================================================== --- Ranked Robin (RCV-RR / Copeland) Method (single winner) --- Tabulating 19 ballots (ranked ballots). Ballots: 5 × D > B > C > A 4 × B > C > A > D 3 × A > D > C > B 3 × A > D > B > C 4 × C > A > B > D Round-Robin — every pair, head-to-head (For – Against): D beats B 11 – 8 D beats C 11 – 8 A beats D 14 – 5 B beats C 12 – 7 A beats B 10 – 9 C beats A 13 – 6 --- Pairwise (Round-Robin) Matrix --- Head-to-head / pairwise comparison — the Ranked Robin tally Legend: For - Equal Support - Against (row vs column) | D | B | C | A | ---------------------------------------------------------------- D > | --- |11 - 0 - 8 |11 - 0 - 8 | 5 - 0 - 14 | B > | 8 - 0 - 11 | --- |12 - 0 - 7 | 9 - 0 - 10 | C > | 8 - 0 - 11 | 7 - 0 - 12 | --- |13 - 0 - 6 | A > | 14 - 0 - 5 |10 - 0 - 9 | 6 - 0 - 13 | --- | Win–loss record — Copeland score = wins + ½·ties (highest score wins; ties broken by total margin, then lot order): # Candidate W–L–T Copeland Margin Beats 1 A 2–1–0 2 +3 D, B 2 D 2–1–0 2 -3 B, C 3 B 1–2–0 1 +1 C 4 C 1–2–0 1 -1 A Winner — Ranked Robin (RCV-RR): A *** 2 candidates tie for the most wins (D, A) — tied on the tally, not a cycle (some of them beat others head-to-head, but no loop closes). Resolved by total margin, then lot order. --- Smith Set (the generalized Condorcet winner) --- The smallest group whose every member beats every candidate outside it — the honest answer to "who is even in contention?". Smith set (4 of 4): D, A, B, C Outside (0): — More than one member ⇒ NO Condorcet winner: the top of the tournament is a cycle, so the strongest "candidate" is a set, not a person. Which member of the set should win is exactly what Minimax / Ranked Pairs / Schulze disagree about — see 05_Ranked_Robin/01_Learn/cycle_resolution.md. Note: the Copeland leaders (D, A) are only part of the set — the win–loss table's top block understates how wide the contention is. Ranked Robin (RCV-RR) winner A is INSIDE the Smith set. ✓ Guaranteed: Ranked Robin (Copeland) is Smith-efficient — every member of the set outscores every outsider, so the top of the win–loss table is always inside the set, however the tie among them is then broken. More: 07_Concepts/topics/smith_set.md