X-Git-Url: http://www.chiark.greenend.org.uk/ucgi/~ian/git?p=appendix-a6.git;a=blobdiff_plain;f=stv;h=fbd7b41050b18f535931223c8b7e0d8534c9f095;hp=9e0aceee2dd826ed83a2187795b809d2bb0d17f1;hb=0328306e06758d9fb43cec21611d044eda1acf09;hpb=b673f3ba34855765aca513ee45b84a918eaad099

diff --git a/stv b/stv
index 9e0acee..fbd7b41 100755
--- a/stv
+++ b/stv
@@ -7,6 +7,10 @@ use strict;
 use utf8;
 use autodie;
 use bigrat;
+use Carp;
+use Data::Dumper;
+use List::Util qw(sum0);
+use List::MoreUtils qw(nsort_by);
 
 # vote is
 #  { Voter => opaque,
@@ -19,10 +23,12 @@ our @allvotes;
 our $places = shift @ARGV;
 die unless $places eq ($places + 0);
 
+open DEBUG, ">.stv.log" or die $!;
+
 while (<>) {
     next if m/^\w+$/;
     m/^(\w+) ([A-Z]+)$/ or die "$_ ?";
-    my $prefs = $1;
+    my $prefs = $2;
     my $vote = {
         Voter => $1,
     	Weight => 1.0,
@@ -33,7 +39,8 @@ while (<>) {
 
 sub pr ($) {
     my ($f) = @_;
-    return sprintf "%10.6f=%-10s", $f, $f;
+    confess unless defined $f;
+    return sprintf "%10.6f = %-10s", $f, $f;
 }
 
 sub votelog ($$) {
@@ -41,67 +48,263 @@ sub votelog ($$) {
     push @{ $vote->{Log} }, "stage $stage: $m";
 }
 
-sub filterout ($$) {
-    my ($cand, $why) = @_;
-    foreach my $vote (@allvotes) {
-	my $oldprefs = $vote->{Prefs};
-	my @prefs = grep { $_ ne $cand } $oldprefs;
-	next if @prefs == @$oldprefs;
-	votelog $vote, "crossed out candidate $cand: $why";
+our @elected; # $elected[] = $candidate
+
+our @unsorted = @allvotes;
+
+our %sorted;
+# $sorted{$firstpref}{Votes} = [ $vote, ... ]
+# $sorted{$firstpref}{Cand} = $firstpref
+# $sorted{$firstpref}{Total} = $totalweight
+our @surpluses; # values same as %sorted
+
+our @exhausted; # votes
+
+our %continuing; # $continuing{$candidate}=1
+
+our @stagerecord; # $stagerecord[]{$candidate} = $total
+
+sub voteliveprefs ($) {
+    my ($vote) = @_;
+    grep { $continuing{$_} } @{ $vote->{Prefs} };
+}
+
+sub votelogfull ($$) {
+    my ($vote,$m) = @_;
+    votelog $vote, $m;
+    votelog $vote, ("continuing prefs: ". join ' ', voteliveprefs $vote);
+}
+
+foreach my $vote (@allvotes) {
+    $continuing{$_}=1 foreach @{ $vote->{Prefs} };
+}
+
+sub equalpiles ($@) {
+    my ($how, @sorted) = @_;
+    return () unless @sorted;
+    my $s = $sorted[0];
+    my $eqtotal = $s->{Total};
+    my $count = 0;
+    while ($count < @sorted && $sorted[$count]{Total} == $eqtotal) {
+	printf "%7s %10s %s\n", $how, $sorted[$count]{Cand},
+	    pr $sorted[$count]{Total};
+	$count++;
     }
+    return @sorted[ 0 .. $count-1 ];
+}
+
+sub historically_prefer ($@) {
+    my ($signum, @choices) = @_;
+
+    return $choices[0] if @choices < 2;
+
+    my $compare = sub {
+	foreach my $sr (@stagerecord) {
+	    my $d = $sr->{ $a->{Cand} } <=> $sr->{ $b->{Cand} };
+	    return $d * $signum if $d;
+	}
+	return 0;
+    };
+
+    @choices = sort $compare, @choices;
+    $a = $choices[0];
+    my $numequal = 0;
+    for (;;) {
+	last unless $numequal >= @choices;
+	$b = $choices[$numequal];
+	last if $compare->();
+    }
+
+    die 'random choice unimplemented' if $numequal > 1;
+    return $choices[0];
+}
+
+foreach my $c (keys %continuing) {
+    $sorted{$c} = {
+        Cand => $c,
+        Votes => [],
+    };
 }
 
 for (;;) {
     $stage++;
 
-    my %sorted;
-    # $sorted{firstpref}{Votes} = [ $vote, ... ]
-    # $sorted{firstpref}{Total} = [ $vote, ... ]
-    for my $vote (@allvotes) {
-	next unless @{ $vote->{Prefs} };
-	my $firstpref = $vote->{Prefs}[0];
-	push @{ $sorted{$firstpref}{Votes} }, $vote;
+    printf "----- stage %d -----\n", $stage;
+
+    print DEBUG "#################### $stage ####################\n",
+	Data::Dumper->Dump(
+[ \@stagerecord, \@elected, \@unsorted, \%sorted, \@surpluses, \%continuing ],
+[qw( _@stagerecord _@elected _@unsorted _%sorted _@surpluses _%continuing )]
+	   );
+
+    my $placesremain = $places - @elected;
+
+    unless ($placesremain > 0) {
+	printf "Complete.\n";
+	last;
+    }
+
+    while (my $vote = shift @unsorted) {
+	my ($firstpref) = voteliveprefs $vote;
+	if (!defined $firstpref) {
+	    votelog $vote, "ballot exhausted";
+	    push @exhausted, $vote;
+	} else {
+	    push @{ $sorted{$firstpref}{Votes} }, $vote;
+	}
     }
     foreach my $firstpref (sort keys %sorted) {
 	foreach my $vote (@{ $sorted{$firstpref}{Votes} }) {
 	    votelog $vote, "counted $vote->{Weight} for $firstpref";
-	    $sorted{$firstpref}{Total} += $vote->{Weight};
 	}
     }
-    my @sorted = sort {
-	$sorted{$b}{Total} <=> $sorted{$a}{Total};
-    } keys %sorted;
+    my @sorted;
+    my $things_update = sub {
+	foreach my $s (@surpluses, values %sorted) {
+	    $s->{Total} = sum0 map { $_->{Weight} } @{ $s->{Votes } };
+	}
+	@sorted = nsort_by { -$_->{Total} } values %sorted;
+    };
+    $things_update->();
+
+    print DEBUG "SORTED\n", Dumper(\@sorted);
+
+    push @stagerecord, { map { ($_->{Cand}, $_->{Total}) } @sorted };
 
     my $totalvalid = 0;
-    foreach my $firstpref (@sorted) {
-	$sorted{$firstpref}{Total} += $_->{Weight}
-	    foreach @{ $sorted{$firstpref}{Votes} };
-	printf "%10s %s\n", $firstpref, pr $sorted{$firstpref}{Total};
-	$totalvalid += $sorted{$firstpref}{Total};
+    my $countvalid = sub {
+	my ($l, $what) = @_;
+	foreach my $s (@$l) {
+	    printf "%-7s %10s %s\n", $what, $s->{Cand}, pr $s->{Total};
+	    $totalvalid += $s->{Total};
+	}
+    };
+    $countvalid->(\@sorted,    '1stpref');
+    $countvalid->(\@surpluses, 'surplus');
+
+    printf "%7s %10s %s\n", 'TOTAL', '-----', pr $totalvalid;
+
+    unless ($totalvalid > 0) {
+	printf "No more votes!\n";
+	last;
+    }
+
+    my $quota = $totalvalid / ($placesremain + 1);
+    printf "%7s %10s %s\n", 'quota', '', pr $quota;
+
+    my $need_to_transfer_surplus = 1;
+
+    # Look for people to elect.
+    # We elect as many as we can, rather than recomputing the (lower) quota
+    # (ERS rules 5.4.9)
+    for (;;) {
+	my $s = $sorted[0];
+	my $topvoters = $s->{Total};
+	my $surplus = $topvoters - $quota;
+	last unless $surplus > 0;
+
+	printf "%7s %10s ***************\n", 'ELECTED', $s->{Cand};
+	push @elected, $s->{Cand};
+
+	my $derate = $topvoters / $surplus;
+	printf "%7s %10s %s\n", 'derate', $s->{Cand}, pr $derate;
+
+	foreach my $vote (@{ $s->{Votes} }) {
+	    votelog $vote, "elected $s->{Cand}, derated $derate";
+	    $vote->{Weight} /= $derate;
+	}
+	push @surpluses, $s;
+	delete $sorted{ $s->{Cand} };
+	delete $continuing{ $s->{Cand} };
+
+	$things_update->();
+	printf "%7s %10s %s\n", 'surplus', $s->{Cand}, pr $s->{Total};
+
+	$need_to_transfer_surplus = 0;
+	# before actually transferring a surplus, we will consider
+	# eliminating, and then reconsider with a lower quota
     }
-    printf "%10s %s\n", 'TOTAL', pr $totalvalid;
 
-    last unless $totalvalid > 0;
+    my $deferredsurplus = sum0 map { $_->{Total} } @surpluses;
+    printf "%18s %s\n", 'deferred surplus', pr $deferredsurplus;
 
-    my $quota = $totalvalid / ($places + 1);
-    printf "\nquota = %10s\n", pr $quota;
+    # Look for people to eliminate
+    # We eliminate before trying to transfer surpluses
+    # ERS 5.2.5
+    my $elimvotebefore = 0;
+    for (;;) {
+	last unless @sorted;
 
-    my $topfirst = $sorted[0];
-    my $topvoters = $sorted{$topfirst}{Weight};
-    my $surplus = $topvoters - $quota;
-    if ($surplus >= 0) {
-	printf "%10s ELECTED\n", $sorted[0];
+	if ($elimvotebefore) {
+	    printf "%18s %s\n", 'elimination, sofar', pr $elimvotebefore;
+	} elsif (@surpluses) {
+	    printf "%18s\n", 'elimination, maybe';
+	} else {
+	    printf "%18s\n", 'elimination, starts';
+	}
+
+	my @elim = equalpiles 'elim?', reverse @sorted;
+	my $elimvotenow = sum0 map { $_->{Total} } @elim;
+
+	if (@surpluses || $elimvotebefore) {
+	    # rule 5.2.2
+	    if (@sorted == @elim) {
+		printf "%18s\n", 'no-elim (all-equal)';
+		last;
+	    }
+	    my $nextup = $sorted[ $#sorted - @elim ];
+	    printf "%7s %10s %s\n", 'nextup', $nextup->{Cand},
+		pr $nextup->{Total};
+	    my $aheadby = $nextup->{Total} - ($elimvotenow + $elimvotebefore);
+	    unless ($deferredsurplus <= $aheadby) {
+		# rule 5.2.2 (b)
+		printf "%18s %s\n", 'no-elim (nextup)', pr $aheadby;
+		last;
+	    }
+	}
 
-	# transfer the surplus
-	my $weightmult = $surplus / $topvoters;
-	foreach my $vote (@{ $sorted{$topfirst}{Votes} }) {
-	    votelog $vote, "part of surplus of weight $weightmult";
-	    $vote->{Weight} *= $weightmult;
+	my $elim_tie =
+	    @elim > 1 &&
+	    (scalar keys %continuing) - (scalar @elim) < $placesremain;
+	if ($elim_tie) {
+	    # eliminate only one then, and try again
+	    printf "elim-tie!\n";
+	    @elim = historically_prefer -1, @elim;
 	}
-	filterout $topfirst, "candidate was elected";
-    } else {
-	my $elim = $sorted{ $#sorted };
-	printf "%10s eliminated\n", $elim;
-	filterout $elim, "candidate was eliminated";
+
+	foreach my $s (@elim) {
+	    my $c = $s->{Cand};
+	    printf "%7s %10s %s\n", 'ELIM', $c, '----------';
+	    my $votes = $s->{Votes};
+	    votelogfull $_, "failed to stop $c elimination" foreach @$votes;
+	    $elimvotebefore += $s->{Total};
+	    delete $continuing{$c};
+	    delete $sorted{$c};
+	    push @unsorted, @$votes;
+	}
+	
+	$things_update->();
+	$need_to_transfer_surplus = 0;
+	last if $elim_tie; # no more, then!
     }
+    
+    next unless $need_to_transfer_surplus;
+
+    @surpluses = nsort_by { $_->{Total} } @surpluses;
+    my @surplusxfer = equalpiles 'xfer?', @surpluses;
+    die unless @surplusxfer;
+
+    if (@surplusxfer > 1) {
+	@surplusxfer = historically_prefer +1, @surplusxfer;
+    }
+
+    my $s = $surplusxfer[0];
+    my $c = $s->{Cand};
+    printf "%7s %10s\n", 'xfer', $c;
+    my $votes = $s->{Votes};
+    votelogfull $_, "surplus transferred" foreach @$votes;
+    @surpluses = grep { $_->{Cand} ne $c } @surpluses;
+    push @unsorted, @$votes;
 }
+
+print "done.\n";