From: Ian Jackson <ijackson@chiark.greenend.org.uk>
Date: Mon, 1 Aug 2016 16:45:39 +0000 (+0100)
Subject: stv: fix tiebreaks
X-Git-Url: http://www.chiark.greenend.org.uk/ucgi/~ian/git?p=appendix-a6.git;a=commitdiff_plain;h=8a14c3d1ae526accda2146e15fc99f98c1b94548

stv: fix tiebreaks
---

diff --git a/stv b/stv
index 3942b6b..03f16d8 100755
--- a/stv
+++ b/stv
@@ -95,18 +95,36 @@ sub equalpiles ($@) {
 
 sub historically_prefer ($@) {
     my ($signum, @choices) = @_;
+    # $signum==+1 means choose candidates with more early preferences
 
     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;
+	    my $d = ($sr->{ $a->{Cand} }//0) <=> ($sr->{ $b->{Cand} }//0);
+	    return -$d * $signum if $d;
 	}
 	return 0;
     };
 
     @choices = sort $compare @choices;
+
+    print DEBUG "historically_prefer\n",
+	Data::Dumper->Dump([\@choices, \@stagerecord],
+			   [qw(_@choices _@stagerecord)]);
+
+    foreach my $s (@choices) {
+	my $c = $s->{Cand};
+	printf " %6s %10s |", 'tiebrk', $c;
+	foreach my $sr (@stagerecord) {
+	    my $p = pr($sr->{$c} // 0);
+	    $p =~ s/\.0+\b//g;
+	    $p =~ s/ //g;
+	    print "$p|";
+	}
+	print "\n";
+    }
+
     $a = $choices[0];
     my $numequal = 1;
     for (;;) {
@@ -161,7 +179,7 @@ for (;;) {
     }
     my @sorted;
     my $things_update = sub {
-	foreach my $s (@surpluses, values %sorted) {
+	foreach my $s (values %sorted) {
 	    $s->{Total} = sum0 map { $_->{Weight} } @{ $s->{Votes } };
 	}
 	@sorted = nsort_by { -$_->{Total} } values %sorted;
@@ -205,6 +223,7 @@ for (;;) {
 	my $topvoters = $s->{Total};
 	my $surplus = $topvoters - $quota;
 	last unless $surplus >= 0;
+	last unless $placesremain;
 
 	my @elect = equalpiles 'elect?', @sorted;
 
@@ -226,6 +245,7 @@ for (;;) {
 	    push @newsurpluses, $s;
 	    delete $sorted{ $s->{Cand} };
 	    delete $continuing{ $s->{Cand} };
+	    $placesremain--;
 	}
 
 	$things_update->();
@@ -245,15 +265,18 @@ for (;;) {
 	    grep { !!voteliveprefs $_ }
 	    @$votes;
 
+	my $derate = 1/1;
 	printf "%7s %10s %s\n", 'xfrable', $s->{Cand}, pr $transferrable;
 	if ($transferrable > $surplus) {
-	    my $derate = $transferrable / $surplus;
+	    $derate = $transferrable / $surplus;
 	    printf "%7s %10s %s\n", 'derate', $s->{Cand}, pr $derate;
 	    foreach my $vote (@{ $s->{Votes} }) {
 		votelog $vote, "part of surplus, derated ". pr $derate;
 		$vote->{Weight} /= $derate;
 	    }
 	}
+	$s->{Total} = $transferrable / $derate;
+
 	push @surpluses, $s;
 
 	$things_update->();