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README.txt
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README.txt
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// VoteFairRanking.cpp or votefair_ranking.cpp
//
// This application calculates VoteFair Ranking results.
// Specifically it calculates:
//
// * VoteFair popularity ranking
//
// * VoteFair representation ranking
//
// * VoteFair party ranking
//
// VoteFair Ranking is described at www.VoteFair.org and in the book
// "Ending The Hidden Unfairness In U.S. Elections" by Richard Fobes.
// The components of VoteFair Ranking that are implemented here are
// briefly described below in the ABOUT section. Additional details
// are explained within the source code.
//
//
// -----------------------------------------------
//
// COPYRIGHT & LICENSE
//
// (c) Copyright 1991 through 2019 by Richard Fobes at www.VoteFair.org.
// You can redistribute and/or modify this VoteFairRanking software
// under the MIT software license terms that appear in the source-code file.
// Also a copy of the license is included in the LICENSE file.
// Conversion of this code into another programming language
// is also covered by these license terms.
//
//
// -----------------------------------------------
//
// VERSION
//
// Version 6.00 - In 2019 Richard Fobes ported
// portions of the Perl library version (5.00)
// into this standalone C++ version.
// See the Perl-version history for earlier
// developments.
//
//
// -----------------------------------------------
//
// USAGE
//
// The following sample code executes this software under a typical
// Windows environment with the g++ compiler and the mingw32 library
// already installed.
//
// path=C:\Program Files (x86)\mingw-w64\i686-8.1.0-posix-dwarf-rt_v6-rev0\mingw32\bin\
//
// g++ votefair_ranking.cpp -o votefair_ranking
//
// .\votefair_ranking < input_votefair_ranking_case_123.txt > output_votefair_ranking_case_123.txt
//
// This usage assumes that file input_votefair_ranking_case_123.txt
// contains appropriately formatted election/survey/poll data for
// case numbered 123, and it writes the coded results to file
// output_votefair_ranking_case_123.txt.
//
// Typically the input file is generated by other software, and
// typically the output file is used as input to other software.
// An example of such software is the "VoteFair-polls" code on
// GitHub (in the CPSolver repository).
//
// The mathematical algorithms of VoteFair Ranking are in the
// public domain.
//
//
// -----------------------------------------------
//
// ABOUT
//
// This software calculates VoteFair Ranking results. The portions
// of VoteFair Ranking implemented here are:
//
// * VoteFair popularity ranking. This voting method calculates the
// full popularity ranking of all candidates (or choices in the case
// of a survey) from most popular and second-most popular down to
// least popular. It uses the preference information collected on
// 1-2-3 ballots or ranked ballots (or any equivalent way of
// expressing "ranked" preferences). When a single position
// is being filled, the most popular candidate is declared the winner.
// This calculation method is mathematically equivalent to the
// Condorcet-Kemeny election method. See below about very rare cases
// when this software can yield results that do not match VoteFair
// popularity ranking.
//
// * VoteFair representation ranking. This voting method is used to
// elect a second candidate who represents the voters who are not
// well-represented by the most-popular candidate, or to fill
// multiple board-of-director positions, or to choose a second
// simultaneous activity in addition to the most popular activity.
// This method reduces the influence of the voters who are already
// well-represented by the most popular candidate (or choice), and
// it does so in a way that protects against strategic voting. If
// instead the second-most popular candidate as identified by
// VoteFair popularity ranking were chosen, the same voters who
// prefer the first winner also can determine the second winner, and
// this can leave large numbers of other voters unrepresented.
// Additional levels of representation ranking can be used to fill
// additional seats, although VoteFair partial-proportional ranking
// should be used instead if "proportional representation" of
// political parties is needed, especially for the purpose of
// defeating attempts to gerrymander district boundaries.
// This ranking provides "proportional representation." It ignores
// political-party associations, yet when used in a governmental
// election the winners are typically from different political
// parties (unless just one party offers great candidates and the
// other parties offer bad candidates).
//
// * VoteFair party ranking. This voting method ranks political
// parties according to a different kind of "popularity". The
// results can be used in high-stakes elections to limit the number
// of candidates allowed by each party. In such cases the two or
// three political parties that are ranked highest can be limited to
// offering just two candidates from each party, and lower-ranked
// parties can be allowed to offer one candidate each, and any
// additional parties can be prohibited from offering any candidate
// (because those parties are too unpopular and too
// unrepresentative). Such limits have not been needed in the past
// because the fear of vote splitting has limited each political
// party to offering just one candidate in each contest.
//
// Note that VoteFair partial-proportional ranking is not calculated
// by this software because it requires knowing the results of many
// elections, and because those results can be calculated using a
// simple spreadsheet.
//
// In addition to being useful for elections, VoteFair Ranking also
// is useful for calculating results for surveys and polls, ranking
// the popularity of songs and movies, and much more.
//
// In mathematical terms, VoteFair Ranking is useful for doing
// "combinatorial optimization" and may be useful for solving the
// "linear ordering problem". See Wikipedia for details about these
// terms.
//
// VoteFair popularity ranking calculations are mathematically
// equivalent to the Condorcet-Kemeny vote-counting method.
//
// Clarification: For reasons of computation time, there are some
// very rare cases for which this software can produce results that
// differ from full VoteFair popularity ranking results.
// These exceptions involve more choices (candidates) than the
// value of the constant named "global_check_all_scores_choice_limit",
// which currently has a default value of 6.
// In those rare cases, the software estimates which top (6) choices
// are the most popular, and then does the full VoteFair popularity
// ranking to determine which of those top choices is most popular.
// The rare cases in which the estimation method produces different
// results involve one or more rock-paper-scissors-like cycles
// that include the top choices, which is a rare combination.
// As an analogy, those cases are like finding the highest
// sand dune in a desert, whereas most cases are like finding
// the highest mountain peak in a mountain range.
// As the number of ballots increases (such as beyond 50 ballots),
// the likelihood of such cycles greatly decreases.
// If this difference is important, the value of the constant
// "global_check_all_scores_choice_limit" can be increased, but
// that change will dramatically increase calculation time,
// to the point of requiring years of computation time for values
// even as small as 20. Therefore, values larger than 12 are not
// recommended.
//
// Additional details about the calculations appear within comments
// in the source-code file.
//
// -----------------------------------------------