X-Git-Url: http://www.chiark.greenend.org.uk/ucgi/~ian/git?p=appendix-a6.git;a=blobdiff_plain;f=stv;h=762da6359ed848ee63833b25f827df381ec128c6;hp=b2ae674f18085097c510c88514c9e54d7b9c300b;hb=530e6a27004910679481ad4a8e52f4beca643c32;hpb=e12fb06eb305bfb6bd29861f6edada00bab8eebe

diff --git a/stv b/stv
index b2ae674..762da63 100755
--- a/stv
+++ b/stv
@@ -7,6 +7,7 @@ use strict;
 use utf8;
 use autodie;
 use bigrat;
+use List::MoreUtils qw(nsort_by);
 
 # vote is
 #  { Voter => opaque,
@@ -20,12 +21,13 @@ our $places = shift @ARGV;
 die unless $places eq ($places + 0);
 
 while (<>) {
-    m/^(\w+) ([A-Z]+)$/ or die;
+    next if m/^\w+$/;
+    m/^(\w+) ([A-Z]+)$/ or die "$_ ?";
     my $prefs = $1;
     my $vote = {
         Voter => $1,
     	Weight => 1.0,
-    	Prefs => (split //, $prefs),
+    	Prefs => [ split //, $prefs ],
     };
     push @allvotes, $vote;
 }
@@ -50,57 +52,180 @@ sub filterout ($$) {
     }
 }
 
+our @elected; # $elected[] = $candidate
+
+our @unsorted = @allvotes;
+
+our %sorted;
+# $sorted{$firstpref}{Votes} = [ $vote, ... ]
+# $sorted{$firstpref}{Cand} = $firstpref
+# $sorted{$firstpref}{Total} = $totalweight
+our @sorted; # values same as %sorted
+our @surpluses; # values same as %sorted
+
+our @exhausted; # votes
+
+our %continuing; # $continuing{$candidate}=1
+
+our @stagerecord; # $stagerecord[]{$candidate} = $total
+
+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\n", $how, $sorted[$count]{Cand};
+	$count++;
+    }
+    
+
 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;
+    while (my $vote = shift @unsorted) {
+	my ($firstpref) = grep { $continuing{$_} } @{ $vote->{Prefs} };
+	if (!defined $firstpref) {
+	    votelog $vote, "ballot exhausted";
+	    push @exhausted, $vote;
+	} else {
+	    push @{ $sorted{$firstpref}{Votes} }, $vote;
+	}
     }
+    $sorted{$_}{Cand} = $_ foreach keys %sorted;
     foreach my $firstpref (sort keys %sorted) {
 	foreach my $vote (@{ $sorted{$firstpref}{Votes} }) {
-	    votelog $vote, "counted $vote->{Weight] for $firstpref";
+	    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 $sort_update = sub {
+	@sorted = nsort_by { -$_->{Total} } values %sorted;
+    };
+    $sort_update->();
+
+    push @stagerecord, { map { ($_->{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 $placesremain = $places - @elected;
+
+    unless ($placesremain > 0) {
+	printf "Complete.\n";
+	last;
     }
-    printf "%10s %s\n", 'TOTAL', pr $totalvalid;
 
-    last unless $totalvalid > 0;
+    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->{Weight};
+	my $surplus = $topvoters - $quota;
+	last unless $surplus > 0;
 
-    my $quota = $totalvalid / ($places + 1);
-    printf "\nquota = %10s\n", pr $quota;
+	printf "%7s %10s\n", 'ELECTED', $s->{Cand};
+	push @elected, $s->{Cand};
 
-    my $topfirst = $sorted[0];
-    my $topvoters = $sorted{  }{Weight};
-    my $surplus = $topvoters - $quota;
-    if ($surplus >= 0) {
-	printf "%10s ELECTED\n", $sorted[0];
+	my $derate = $topvoters / $surplus;
+	printf "%7s %10s\n", 'derate', $s->{Cand}, pr $derate;
 
-	# transfer the surplus
-	my $weightmult = $surplus / $topvoters;
-	foreach my $vote (@{ $sorted{$topfirst}{Votes} }) {
-	    votelog $vote, "part of surplus of weight $weightmult";
-	    $vote->{Weight} *= $weightmult;
+	foreach my $vote (@{ $s->{Votes} }) {
+	    votelog $vote, "elected $s->{Cand}, derated $weightmult";
+	    $vote->{Weight} /= $derate;
 	}
-	filterout $topfirst, "candidate was elected";
-    } else {
-	my $elim = $sorted{ $#sorted };
-	printf "%10s eliminated\n", $elim;
-	filterout $elim, "candidate was eliminated";
+	push @surpluses, $s;
+	delete %sorted{ $s->{Cand} };
+	delete $continuing{ $s->{Cand} };
+
+	$sort_update->();
+	$need_to_transfer_surplus = 0;
+	# before actually transferring a surplus, we will consider
+	# eliminating, and then reconsider with a lower quota
     }
+
+    my $deferredsurplus = sum map { $_->{Total} } @surpluses;
+    printf "%7s %10s %s\n", 'def.srp', 'total', pr $deferredsurplus;
+
+    # Look for people to eliminate
+    # We eliminate before trying to transfer surpluses
+    # ERS 5.2.5
+    for (;;) {
+	last unless @sorted;
+
+	my @elim = equalpiles 'elim?', reverse @sorted;
+	my $elimvote = sum map { $_->{Total} } @elim;
+	my $elimvotetotal = $elimvote * scalar @elim;
+
+	if (@surpluses and $elimvotetotal > $deferredsurplus) {
+	    printf "no-elim, un-defer\n";
+	    last;
+	}
+
+	if ((scalar keys %continuing) - (scalar @elim) < $placesremain) {
+	    # eliminate only one then, and try again
+	    printf "elim-tie!\n";
+	    @elim = historically_prefer -1, @elim;
+	}
+
+	foreach my $s (@elim) {
+	    my $c = $s->{Cand};
+	    printf "%7s %10s\n", 'ELIM', $c;
+	    my $votes = $s->{Votes};
+	    votelog $_, "failed to stop $c elimination" foreach @$votes;
+	    delete %continuing{$c};
+	    delete %sorted{$c};
+	    push @unsorted, @$votes;
+	}
+	
+	$sort_update->();
+	$need_to_transfer_surplus = 0;
+    }
+    
+    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};
+    votelog $_, "surplus transferred" foreach @$votes;
+    @surpluses = grep { $_->{Cand} ne $c } @surpluses;
+    push @unsorted, @$votes;
 }
+
+print "done.\n";