Projects / Condorcet with Dual Dropping

Condorcet with Dual Dropping

Condorcet with Dual Dropping is a ranking system for deciding single or multi-winner contests (elections) using voted preference (or approval) ballot list or pairwise tally matrix. It computes the Cloneproof Schwartz Sequential Dropping (CSSD) and Tideman's Ranked Pair (RP) results for each contest round, and selects the combined CSSD and RP outcome with the lowest overall dropping cost. There are options to compute just the CSSD, RP, or Minimum Dropping Cost outcome, various optional pair rank and winner tie-breakers, and alternative measures of dropping cost (winning votes and/or margin). It comes as a console program and CGI executable.

Operating Systems

Recent releases

  •  28 Jun 2004 03:37

    Release Notes: A problem with the findCycles subroutine has been fixed. The $CGI_in variable is set in the script to enable execution via an HTML form. A sample HTML form is included. The --HTML_out command outputs HTML. The --show_TBR command displays the TieBreak Rank file contents. The Graph module is included in the lib subdirectory.

    •  19 Jun 2004 19:46

      Release Notes: Graph module version 0.20105 is now used. A failure to reset ignore attributes after RP was corrected, which could impact the CSSD result. Other minor bugfixes were made. Only those drops that contribute to selecting the winner(s) are now included in the dropping cost. Single --verbose now displays round results and branching information. The activity bar is turned off if the --verbose command is utilized.

      •  06 Jun 2004 10:11

        Release Notes: SSD was converted to Cloneproof SSD (CSSD). Various options were added, including --nountierank_margins for skipping margin pair ranking tiebreaker, --noTBR_tiebreak, which skips the winner tiebreaker, --nountierank_TBR, which skips the pair ranking tiebreaker, and --majority_first and --majority_approval commands that declare majority first and majority approval winners after the initial beats all. The --eachround_tiebreak option executes the option winner tiebreakers every round that has a tie. A script that creates TieBreak Rank (TBR) files was included.

        •  31 May 2004 01:55

          Release Notes: A couple of bugs were corrected in, including one that could corrupt the results.

          •  25 Jan 2004 11:42

            No changes have been submitted for this release.

            Recent comments

            14 Sep 2002 18:34 051xmcumxaaqitwosz1g

            General information documentation
            SSD, RP, DD explanations (

            Choosing Approval and/or Preference Ballots (

            Approval Cutoff in Preference Ballots (a href=


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