X-Git-Url: http://www.chiark.greenend.org.uk/ucgi/~ian/git?p=appendix-a6.git;a=blobdiff_plain;f=compute-scottish-stv;h=6fde10308b409753d9f877e1df709300d2558fa3;hp=78e62fb56bb7e4651f57b10d1d228a1030c429da;hb=a4f2fc687bb9e16c33a59619acafe2cc21833ee1;hpb=2ca665096a98105791c0d59b9bb0fae765c909b4

diff --git a/compute-scottish-stv b/compute-scottish-stv
old mode 100644
new mode 100755
index 78e62fb..6fde103
--- a/compute-scottish-stv
+++ b/compute-scottish-stv
@@ -4,6 +4,9 @@
 # The Scottish Local Government Elections Order 2007
 
 use strict;
+use Carp;
+use Data::Dumper;
+use Math::BigRat;
 use bigrat;
 
 # Data structures:
@@ -22,10 +25,25 @@ use bigrat;
 
 our $seats=0;
 
+our @allvotes;
+our @non_transferable;
+our %cands;
 our $stage=0;
 our $quota;
 our %tie;
 
+open DEBUG, ">.compute.log" or die $!;
+DEBUG->autoflush(1);
+
+$SIG{__WARN__} = sub {
+    print DEBUG Dumper(\%tie,
+		       \@non_transferable,
+		       \%cands,
+		       \@allvotes,
+		       $stage, $quota);
+    confess $_[0];
+};
+
 sub unkopt ($$) {
     my ($what,$opt) = @_;
     if ($opt =~ m/^[A-Z]/) {
@@ -52,16 +70,16 @@ for (;;) {
 	    }
 	}
     } elsif (m/^(\w+) = (\S*) \|/) {
-	my ($cand,$desc) = @_;
+	my ($cand,$desc) = ($1,$2);
 	unkopt "candidate $cand", $_ foreach split / /, $';
 	$cands{$cand}{Desc} = $desc;
     } elsif (m/^(\w*) :\s*(.*)\s*\|(.*)/) {
 	my ($voter,$prefs,$opts) = ($1,$2,$3);
-	$v = { Voter => $voter };
+	my $v = { Voter => $voter, Prefs => [ ] };
 	push @{ $v->{Prefs} }, [ $_ =~ m/\w+/g ]
 	    foreach split /\s+/, $prefs;
 	foreach $_ (split / /, $opts) {
-	    if (m/^_?[Ww]eight=(\d+)/(\d+)$/) {
+	    if (m/^_?[Ww]eight=(\d+)\/(\d+)$/) {
 		$v->{Weight} = $1 / $2;
 	    } elsif (m/^_?[Ww]eight=([0-9.]+)$/) {
 		$v->{Weight} = new Math::BigRat $1;
@@ -77,8 +95,16 @@ for (;;) {
     }
 }
 
-$cands{$_}{Cand} = $_foreach keys %cands;
+$cands{$_}{Cand} = $_ foreach keys %cands;
+$_->{Weight} //= 1/1 foreach @allvotes;
+$_->{TransferredSurplus} //= [ ] foreach @allvotes;
+
+sub votelog ($$) {
+    my ($vote,$m) = @_;
+    push @{ $vote->{Log} }, "stage $stage: $m";
+}
 
+sub sortballots (@);
 sub sortballots (@) {
     # Takes each argument, which should be a ballot, sorts
     # it into $cand{CAND}{Votes} according to first preference.
@@ -89,88 +115,148 @@ sub sortballots (@) {
 	my $firstprefs = shift @{ $v->{Prefs} };
 	my $w = $v->{Weight};
 	if (!$firstprefs || !@$firstprefs) {
-	    vlog $v, "no more preferences, non transferable";
+	    votelog $v, "no more preferences, non transferable";
 	    push @non_transferable, $v;
 	    next;
 	}
 	if (@$firstprefs > 1) {
-	    vlog $v, "splitting due to several equal first preferences";
+	    votelog $v, "splitting due to several equal first preferences";
 	    foreach my $fpref (@$firstprefs) {
 		my $v2 = {
 		    %$v,
 		    Weight => $w / @$firstprefs,
 		    Prefs => [ [ $fpref ], @{ $v->{Prefs} } ],
                 };
-		vlog $v, "split for $fpref";
+		votelog $v, "split for $fpref";
 	    }
 	    next;
 	}
-	my $fp = $firstprefs[0];
+	my $fp = $firstprefs->[0];
 	my $c = $cands{$fp};
 	my $noncont = $c->{NonCont};
 	if ($noncont) {
-	    vlog $v, "dropping pref $fp, $noncont";
-	    sortvallots $v;
+	    votelog $v, "dropping pref $fp, $noncont";
+	    sortballots $v;
 	    next;
 	}
-	vlog $v, "sorted into pile for candidate $fp weight $w";
+	votelog $v, "sorted into pile for candidate $fp weight $w";
 	push @{ $c->{Votes} }, $v;
     }
 }
 
 sub prf {
     my $fmt = shift;
-    printf "stage %d: ".$_, $stage, @_;
+    printf "stage %d: ".$fmt, $stage, @_;
 }
 
 sub countballots () {
-    foreach my $c (values %cand) {
-	$c->{Total} = 0;
-	$c->{Total} += $_->{Weight} foreach @{ $c->{Voters} };
-    }
-    foreach my $cand (sort keys %cand) {
-	$c = $cands{$cand};
+    foreach my $cand (sort keys %cands) {
+	my $c = $cands{$cand};
 	next if $c->{NonCont};
-	prf "cand %s: %s votes\n", $stage, $cand, $c->{Total};
+	$c->{Total} = 0;
+	$c->{Total} += $_->{Weight} foreach @{ $c->{Votes} };
+	prf "candidate %-10s: %10s votes\n", $cand, $c->{Total};
 	$c->{History}[$stage-1] = $c->{Total};
     }
 }
 
 sub computequota () {
     my $totalvalid = 0;
-    $totalvalid += $_->{Total} foreach keys %cands;
-    $quota = floor($totalvalid / (1 + $seats));
+    $totalvalid += $_->{Total} foreach values %cands;
+    $quota = ($totalvalid / (1 + $seats)) -> bfloor();
+    prf "quota %10s\n", $quota;
 }
 
 sub total_history_cmp () {
     my $ha = $a->{History};
     my $hb = $b->{History};
-    foreach my $s (reverse 1 .. $stage) {
+    foreach my $s (reverse 0 .. $stage-1) {
 	my $d = $ha->[$s] <=> $hb->[$s];
 	next unless $d;
-	print DEBUG "history cmp $a->{Cand} $b->[Cand}"
-	    ." => $d (#$s $ha->[$s] $hb->[$s])\n";
-	return $e;
+	print DEBUG "history cmp $a->{Cand} $b->{Cand}".
+	    " => $d (#$s $ha->[$s] $hb->[$s])\n";
+	return $d;
     }
     return 0;
 }
 
+sub continuing () {
+    grep { !$_->{NonCont} } values %cands;
+}
+
+sub select_best_worst ($$$$) {
+    my ($wantcand, $wanttiebreak, $signum, $what) = @_;
+    # $wantcand->($c) = boolish
+    # $wanttiebreak->($total) = boolish
+    # Firstly candidates not meeting $wantcand are ignored
+    # Then we pick the best (worst) candiate by Total (or vote history).
+    # (SLGEO 49(2) and 51(2).
+    # If this does not help then totals are equal and we call wanttiebreak.
+    # If it returns 0 we return alphabetically first CAND.  Otherwise
+    # we tie break.
+
+    my @maybe = grep { $wantcand->($_) } continuing();
+    @maybe = sort total_history_cmp @maybe;
+    @maybe = reverse @maybe if $signum > 0;
+
+    return undef unless @maybe;
+
+    my $nequal = 1;
+
+    for (;;) {
+	my $nextc = $maybe[$nequal];
+
+	# Only interested in those who compare equal according to the
+	# history (SLGEO 49(2)); NB our history includes the current
+	# round.
+	
+	last if $signum*($a = $maybe[0], $b = $nextc, total_history_cmp) > 0;
+	$nextc++;
+    }
+
+    if ($nequal > 1 && !$wanttiebreak->($maybe[0]{Total})) {
+	# ... if equal for election we can do them one by one, since
+	# order does not matter (SLGEO 49 talks about `two or more
+	# ... exceeds').
+	$nequal = 1;
+    }
+
+    my $selectcand;
+    if ($nequal > 1) {
+	my @all = map { $_->{Cand} } @maybe[0 .. $nequal-1];
+	my $tiekey = $signum > 0 ? 'Win' : 'Lose';
+	$selectcand = $tie{"@all"}{$tiekey};
+	die "need tie break, want $tiekey from @all"
+	    unless defined $selectcand;
+	prf "$what %s due to tie break amongst %s\n",
+	    $selectcand, "@all";
+    } else {
+	$selectcand = $maybe[0]{Cand};
+	prf "$what %s\n", $selectcand;
+    }
+
+    return $cands{$selectcand};
+}
+
 sub elect_core ($) {
     my ($c) = @_;
     prf "*** ELECT %s \`%s' ***\n", $c->{Cand}, $c->{Desc};
     $c->{NonCont} = 'Elected';
 }
 
+$stage = 1;
+
 sortballots @allvotes;
+countballots();
+computequota();
 
 for (;;) {
     $stage++;
 
-    my @continuing = grep { !$_->{NonCont} } values %cands;
     my $seats_remain = $seats
-	- grep { $_->{NonCont} eq 'Elected' } values %cands;
-    if (@continuing <= $seats_remain) {
-	foreach my $c (@continuing) {
+	- grep { ($_->{NonCont} // '') eq 'Elected' } values %cands;
+    if (continuing() <= $seats_remain) {
+	foreach my $c (continuing()) {
 	    prf "electing %s to fill remaining place(s)\n", $c->{Cand};
 	    elect_core $c;
 	}
@@ -178,43 +264,15 @@ for (;;) {
     }
 
     countballots();
-    
-    my @maybe_elect = reverse sort total_history_cmp @continuing;
-    my $nelect=0;
-    for (;;) {
-	my $nextc = $maybe_elect[$nelect];
 
-	# We certainly only consider those who meet quota
-	last unless $nextc->{Total} >= $quota;
-	last unless $nextc->{Total} > $quota && $nextel;
-	# ... if equal we can do them one by one, since order
-	# does not matter (SLGEO 49 talks about `two or more ... exceeds')
-
-	last if $nelect &&
-	    (total_history_cmp $maybe_elect[0], $nextc) > 0;
-	# ... only interested in those who compare equal
-	# according ot the history (SLGEO 49(2)); NB our history
-	# includes the current round.
-
-	$nelect++;
-    }
-
-    if ($nelect) {
-	my $electcand;
-	if ($nelect > 1) {
-	    my @all = map { $_->{Cand} } @maybe_elect[0 .. $nelect-1];
-	    my $elect = $tie{"@all"}{Win};
-	    die "need tie break, want winner from @all" unless defined $win;
-	    prf "electing %s due to tie break amongst %s\n",
-		$electcand, "@all";
-	} else {
-	    $electcand = $maybe_elect[0];
-	    prf "electing %s\n";
-	}
+    my $c = select_best_worst
+	sub { $_->{Total} >= $quota },
+	sub { $_ > $quota },
+	+1, 'electing';
 
-	my $c = $cands{$electcand};
+    if ($c) {
 	elect_core $c;
-	votelog $_, "helped elect $electcand" foreach @{ $c->{Votes} };
+	votelog $_, "helped elect $c->{Cand}" foreach @{ $c->{Votes} };
 	
 	# SLGEO 48
 	my $surplus = $c->{Total} - $quota;
@@ -224,16 +282,30 @@ for (;;) {
 	    next;
 	}
 
-	my $B = $c->{Weight};
+	my $B = $c->{Total};
+	my %tspr;
+
+	prf "surplus %10s\n", $surplus;
 
 	foreach my $v (@{ $c->{Votes} }) {
+	    my $previously = $v->{TransferredSurplus};
+	    push @$previously, $c->{Cand};
+
 	    my $A = $surplus * $v->{Weight};
 	    my $F = 100000;
-	    my $xfervalue = floor(($A * $F) / $B) / $f;
+	    my $xfervalue = ((($A * $F) / $B) -> bfloor() ) / $F;
 	    # SLGEO 48(3): we do arithmetic to 5 d3ecimal places,
 	    # but always rounding down
 	    votelog $v, "transferring with value $xfervalue (A=$A B=$B)";
 	    $v->{Weight} = $xfervalue;
+
+	    if (defined $tspr{"@$previously"}) {
+		die unless $tspr{"@$previously"} == $xfervalue;
+	    } else {
+		$tspr{"@$previously"} = $xfervalue;
+		prf "transfer value of ballots %s: %10s\n",
+		    "@$previously", $xfervalue;
+	    }
 	    sortballots $v;
 	}
 	$c->{Votes} = { }; # will crash if we access it again
@@ -241,3 +313,18 @@ for (;;) {
     }
 
     # No-one to elect, must eliminate
+    $c = select_best_worst
+	sub { 1; },
+	sub { 1; },
+	-1, 'eliminating';
+
+    if ($c) {
+	prf "=== eliminating %s (%s) ===\n", $c->{Cand}, $c->{Desc};
+	$c->{NonCont} = 'Eliminated';
+	next;
+    }
+
+    die;
+}
+
+print "done.\n";