Implement Wright STV

html/index.html

@@ -41,7 +41,7 @@
 						<option value="meek06">Meek STV (2006)</option>
 						<option value="meeknz">Meek STV (New Zealand)</option>
 						<option value="senate">Australian Senate STV</option>
-						<!--<option value="wright">Wright STV</option>-->
+						<option value="wright">Wright STV</option>
 						<option value="prsa77">PRSA 1977</option>
 						<option value="ers97">ERS97</option>
 					</select>
@@ -112,7 +112,7 @@
 								<option value="single_stage" selected>Single stage</option>
 								<option value="by_value">By value</option>
 								<option value="parcels_by_order">By parcel (by order)</option>
-								<!--<option value="wright">Wright method (re-iterate)</option>-->
+								<option value="wright">Wright method (re-iterate)</option>
 							</select>
 						</label>
 						<label style="margin-left:1em;">

html/index.js

@@ -460,6 +460,28 @@ function changePreset() {
 		document.getElementById('selPapers').value = 'both';
 		document.getElementById('selExclusion').value = 'by_value';
 		document.getElementById('selTies').value = 'backwards,random';
+	} else if (document.getElementById('selPreset').value === 'wright') {
+		document.getElementById('selQuotaCriterion').value = 'geq';
+		document.getElementById('selQuota').value = 'droop';
+		document.getElementById('selQuotaMode').value = 'static';
+		//document.getElementById('chkBulkElection').checked = true;
+		document.getElementById('chkBulkExclusion').checked = true;
+		document.getElementById('chkDeferSurpluses').checked = false;
+		document.getElementById('selNumbers').value = 'fixed';
+		document.getElementById('txtDP').value = '5';
+		document.getElementById('txtPPDP').value = '2';
+		document.getElementById('chkNormaliseBallots').checked = false;
+		document.getElementById('chkRoundQuota').checked = true;
+		document.getElementById('txtRoundQuota').value = '0';
+		document.getElementById('chkRoundVotes').checked = false;
+		document.getElementById('chkRoundTVs').checked = false;
+		document.getElementById('chkRoundWeights').checked = false;
+		document.getElementById('selSumTransfers').value = 'single_step';
+		document.getElementById('selSurplus').value = 'by_size';
+		document.getElementById('selTransfers').value = 'wig';
+		document.getElementById('selPapers').value = 'both';
+		document.getElementById('selExclusion').value = 'wright';
+		document.getElementById('selTies').value = 'random';
 	} else if (document.getElementById('selPreset').value === 'prsa77') {
 		document.getElementById('selQuotaCriterion').value = 'geq';
 		document.getElementById('selQuota').value = 'droop';

html/main.css

@@ -106,6 +106,10 @@ tr.stage-no td:not(:empty), tr.transfers td {
 tr.info:last-child td, .bb {
 	border-bottom: 1px solid #76858c;
 }
+.blw {
+	/* Used to separate counts in Wright STV */
+	border-left: 2px solid #76858c;
+}
 
 /* Table stripes */
 

src/stv/gregory.rs

@@ -63,7 +63,8 @@ where
 	let quota = state.quota.as_ref().unwrap();
 	let mut has_surplus: Vec<(&Candidate, &CountCard<N>)> = state.election.candidates.iter() // Present in order in case of tie
 		.map(|c| (c, state.candidates.get(c).unwrap()))
-		.filter(|(_, cc)| &cc.votes > quota)
+		//.filter(|(_, cc)| &cc.votes > quota)
+		.filter(|(_, cc)| &cc.votes > quota && cc.parcels.iter().any(|p| !p.is_empty()))
 		.collect();
 	
 	if !has_surplus.is_empty() {
@@ -337,6 +338,8 @@ where
 	count_card.votes.assign(state.quota.as_ref().unwrap());
 	checksum -= surplus;
 	
+	count_card.parcels.clear(); // Mark surpluses as done
+	
 	// Update loss by fraction
 	state.loss_fraction.transfer(&-checksum);
 }
@@ -435,6 +438,7 @@ where
 			checksum -= &votes_transferred;
 			count_card.transfer(&-votes_transferred);
 		}
+		_ => panic!()
 	}
 	
 	if !votes.is_empty() {
@@ -494,3 +498,59 @@ where
 	// Update loss by fraction
 	state.loss_fraction.transfer(&-checksum);
 }
+
+/// Perform one stage of a candidate exclusion according to the Wright method
+pub fn wright_exclude_candidates<'a, N: Number>(state: &mut CountState<'a, N>, opts: &STVOptions, excluded_candidates: Vec<&'a Candidate>)
+where
+	for<'r> &'r N: ops::Sub<&'r N, Output=N>,
+	for<'r> &'r N: ops::Mul<&'r N, Output=N>,
+	for<'r> &'r N: ops::Div<&'r N, Output=N>,
+{
+	// Used to give bulk excluded candidate the same order_elected
+	let order_excluded = state.num_excluded + 1;
+	
+	for excluded_candidate in excluded_candidates.iter() {
+		let count_card = state.candidates.get_mut(excluded_candidate).unwrap();
+		
+		// Rust borrow checker is unhappy if we try to put this in exclude_hopefuls ??!
+		if count_card.state != CandidateState::Excluded {
+			count_card.state = CandidateState::Excluded;
+			state.num_excluded += 1;
+			count_card.order_elected = -(order_excluded as isize);
+		}
+	}
+	
+	// Reset count
+	for (_, count_card) in state.candidates.iter_mut() {
+		if count_card.order_elected > 0 {
+			count_card.order_elected = 0;
+		}
+		count_card.parcels.clear();
+		count_card.votes = N::new();
+		count_card.transfers = N::new();
+		count_card.state = match count_card.state {
+			CandidateState::Withdrawn => CandidateState::Withdrawn,
+			CandidateState::Excluded => CandidateState::Excluded,
+			_ => CandidateState::Hopeful,
+		};
+	}
+	
+	state.exhausted.votes = N::new();
+	state.exhausted.transfers = N::new();
+	state.loss_fraction.votes = N::new();
+	state.loss_fraction.transfers = N::new();
+	
+	state.num_elected = 0;
+	
+	let orig_title = state.title.clone();
+	
+	// Redistribute first preferences
+	super::distribute_first_preferences(state, opts);
+	
+	state.kind = Some("Exclusion of");
+	state.title = orig_title;
+	
+	// Trigger recalculation of quota within stv::count_one_stage
+	state.quota = None;
+	state.vote_required_election = None;
+}

src/stv/mod.rs

@@ -160,6 +160,7 @@ impl STVOptions {
 				"single_stage" => ExclusionMethod::SingleStage,
 				"by_value" => ExclusionMethod::ByValue,
 				"parcels_by_order" => ExclusionMethod::ParcelsByOrder,
+				"wright" => ExclusionMethod::Wright,
 				_ => panic!("Invalid --exclusion"),
 			},
 			meek_nz_exclusion,
@@ -360,6 +361,8 @@ pub enum ExclusionMethod {
 	ByValue,
 	/// Transfer the ballot papers of an excluded candidate parcel by parcel in the order received
 	ParcelsByOrder,
+	/// Wright method (re-iterate)
+	Wright,
 }
 
 impl ExclusionMethod {
@@ -369,6 +372,7 @@ impl ExclusionMethod {
 			ExclusionMethod::SingleStage => "--exclusion single_stage",
 			ExclusionMethod::ByValue => "--exclusion by_value",
 			ExclusionMethod::ParcelsByOrder => "--exclusion parcels_by_order",
+			ExclusionMethod::Wright => "--exclusion wright",
 		}.to_string()
 	}
 }
@@ -952,6 +956,8 @@ where
 			// Exclusion in parts compatible only with Gregory method
 			gregory::exclude_candidates(state, opts, excluded_candidates);
 		}
+		ExclusionMethod::Wright => {
+			gregory::wright_exclude_candidates(state, opts, excluded_candidates);
 		}
 	}
 }

src/stv/wasm.rs

@@ -285,43 +285,52 @@ fn init_results_table<N: Number>(election: &Election<N>, opts: &stv::STVOptions)
 /// Generate subsequent columns of the HTML results table
 fn update_results_table<N: Number>(stage_num: usize, state: &CountState<N>, opts: &stv::STVOptions) -> Array {
 	let result = Array::new();
-	result.push(&format!(r#"<td>{}</td>"#, stage_num).into());
+	
-	result.push(&format!(r#"<td>{}</td>"#, state.kind.unwrap_or("")).into());
+	// Insert borders to left of new exclusions in Wright STV
-	result.push(&format!(r#"<td>{}</td>"#, state.title).into());
+	let mut tdclasses1 = "";
+	let mut tdclasses2 = "";
+	if opts.exclusion == stv::ExclusionMethod::Wright && state.kind == Some("Exclusion of") {
+		tdclasses1 = r#" class="blw""#;
+		tdclasses2 = r#"blw "#;
+	}
+	
+	result.push(&format!(r#"<td{}>{}</td>"#, tdclasses1, stage_num).into());
+	result.push(&format!(r#"<td{}>{}</td>"#, tdclasses1, state.kind.unwrap_or("")).into());
+	result.push(&format!(r#"<td{}>{}</td>"#, tdclasses1, state.title).into());
 	for candidate in state.election.candidates.iter() {
 		let count_card = state.candidates.get(candidate).unwrap();
 		if count_card.state == stv::CandidateState::Elected {
-			result.push(&format!(r#"<td class="count elected">{}</td>"#, pp(&count_card.transfers, opts.pp_decimals)).into());
+			result.push(&format!(r#"<td class="{}count elected">{}</td>"#, tdclasses2, pp(&count_card.transfers, opts.pp_decimals)).into());
-			result.push(&format!(r#"<td class="count elected">{}</td>"#, pp(&count_card.votes, opts.pp_decimals)).into());
+			result.push(&format!(r#"<td class="{}count elected">{}</td>"#, tdclasses2, pp(&count_card.votes, opts.pp_decimals)).into());
 		} else if count_card.state == stv::CandidateState::Excluded {
-			result.push(&format!(r#"<td class="count excluded">{}</td>"#, pp(&count_card.transfers, opts.pp_decimals)).into());
+			result.push(&format!(r#"<td class="{}count excluded">{}</td>"#, tdclasses2, pp(&count_card.transfers, opts.pp_decimals)).into());
 			if count_card.votes.is_zero() {
-				result.push(&r#"<td class="count excluded">Ex</td>"#.into());
+				result.push(&format!(r#"<td class="{}count excluded">Ex</td>"#, tdclasses2).into());
 			} else {
-				result.push(&format!(r#"<td class="count excluded">{}</td>"#, pp(&count_card.votes, opts.pp_decimals)).into());
+				result.push(&format!(r#"<td class="{}count excluded">{}</td>"#, tdclasses2, pp(&count_card.votes, opts.pp_decimals)).into());
 			}
 		} else if count_card.state == stv::CandidateState::Withdrawn {
-			result.push(&r#"<td class="count excluded"></td>"#.into());
+			result.push(&format!(r#"<td class="{}count excluded"></td>"#, tdclasses2).into());
-			result.push(&r#"<td class="count excluded">WD</td>"#.into());
+			result.push(&format!(r#"<td class="{}count excluded">WD</td>"#, tdclasses2).into());
 		} else {
-			result.push(&format!(r#"<td class="count">{}</td>"#, pp(&count_card.transfers, opts.pp_decimals)).into());
+			result.push(&format!(r#"<td class="{}count">{}</td>"#, tdclasses2, pp(&count_card.transfers, opts.pp_decimals)).into());
-			result.push(&format!(r#"<td class="count">{}</td>"#, pp(&count_card.votes, opts.pp_decimals)).into());
+			result.push(&format!(r#"<td class="{}count">{}</td>"#, tdclasses2, pp(&count_card.votes, opts.pp_decimals)).into());
 		}
 	}
-	result.push(&format!(r#"<td class="count">{}</td>"#, pp(&state.exhausted.transfers, opts.pp_decimals)).into());
+	result.push(&format!(r#"<td class="{}count">{}</td>"#, tdclasses2, pp(&state.exhausted.transfers, opts.pp_decimals)).into());
-	result.push(&format!(r#"<td class="count">{}</td>"#, pp(&state.exhausted.votes, opts.pp_decimals)).into());
+	result.push(&format!(r#"<td class="{}count">{}</td>"#, tdclasses2, pp(&state.exhausted.votes, opts.pp_decimals)).into());
-	result.push(&format!(r#"<td class="count">{}</td>"#, pp(&state.loss_fraction.transfers, opts.pp_decimals)).into());
+	result.push(&format!(r#"<td class="{}count">{}</td>"#, tdclasses2, pp(&state.loss_fraction.transfers, opts.pp_decimals)).into());
-	result.push(&format!(r#"<td class="count">{}</td>"#, pp(&state.loss_fraction.votes, opts.pp_decimals)).into());
+	result.push(&format!(r#"<td class="{}count">{}</td>"#, tdclasses2, pp(&state.loss_fraction.votes, opts.pp_decimals)).into());
 	
 	// Calculate total votes
 	let mut total_vote = state.candidates.values().fold(N::zero(), |acc, cc| { acc + &cc.votes });
 	total_vote += &state.exhausted.votes;
 	total_vote += &state.loss_fraction.votes;
-	result.push(&format!(r#"<td class="count">{}</td>"#, pp(&total_vote, opts.pp_decimals)).into());
+	result.push(&format!(r#"<td class="{}count">{}</td>"#, tdclasses2, pp(&total_vote, opts.pp_decimals)).into());
 	
-	result.push(&format!(r#"<td class="count">{}</td>"#, pp(state.quota.as_ref().unwrap(), opts.pp_decimals)).into());
+	result.push(&format!(r#"<td class="{}count">{}</td>"#, tdclasses2, pp(state.quota.as_ref().unwrap(), opts.pp_decimals)).into());
 	if opts.quota_mode == stv::QuotaMode::ERS97 {
-		result.push(&format!(r#"<td class="count">{}</td>"#, pp(state.vote_required_election.as_ref().unwrap(), opts.pp_decimals)).into());
+		result.push(&format!(r#"<td class="{}count">{}</td>"#, tdclasses2, pp(state.vote_required_election.as_ref().unwrap(), opts.pp_decimals)).into());
 	}
 	
 	return result;