Correctly compute vote required for election when using different quotas/quota criteria

src/election.rs

@@ -165,7 +165,7 @@ pub struct CountState<'a, N: Number> {
 	pub quota: Option<N>,
 	/// Vote required for election
 	///
-	/// With a static quota, this is equal to the quota. With ERS97 rules, this may vary from the quota.
+	/// Only used in ERS97/ERS76, or if early bulk election is enabled and there is 1 vacancy remaining.
 	pub vote_required_election: Option<N>,
 	
 	/// Number of candidates who have been declared elected

src/stv/mod.rs

@@ -670,7 +670,8 @@ fn update_vre<N: Number>(state: &mut CountState<N>, opts: &STVOptions) {
 	});
 	log.push_str(format!("Total active vote is {:.dps$}, so the vote required for election is ", total_active_vote, dps=opts.pp_decimals).as_str());
 	
-	let vote_req = total_to_quota(total_active_vote, state.election.seats - state.num_elected, opts); // FIXME: This is incorrect
+	//let vote_req = total_to_quota(total_active_vote, state.election.seats - state.num_elected, opts);
+	let vote_req = total_active_vote / N::from(state.election.seats - state.num_elected + 1);
 	
 	if &vote_req < state.quota.as_ref().unwrap() {
 		// VRE is less than the quota
@@ -746,17 +747,14 @@ fn calculate_quota<N: Number>(state: &mut CountState<N>, opts: &STVOptions) {
 				// Early bulk election and one seat remains: VRE is majority of total active vote
 				update_vre(state, opts);
 			} else {
-				// VRE is quota
-				if state.vote_required_election.is_none() {
-					state.vote_required_election = state.quota.clone();
-				}
+				// No use of VRE
 			}
 		}
 	}
 }
 
-/// Determine if the given candidate meets the quota, according to [STVOptions::quota_criterion]
-fn meets_quota<N: Number>(quota: &N, count_card: &CountCard<N>, opts: &STVOptions) -> bool {
+/// Compare the candidate's votes with the specified target according to [STVOptions::quota_criterion]
+fn cmp_quota_criterion<N: Number>(quota: &N, count_card: &CountCard<N>, opts: &STVOptions) -> bool {
 	match opts.quota_criterion {
 		QuotaCriterion::GreaterOrEqual => {
 			return count_card.votes >= *quota;
@@ -767,13 +765,26 @@ fn meets_quota<N: Number>(quota: &N, count_card: &CountCard<N>, opts: &STVOption
 	}
 }
 
+/// Determine if the given candidate meets the vote required to be elected, according to [STVOptions::quota_criterion] and [STVOptions::quota_mode]
+fn meets_vre<N: Number>(state: &CountState<N>, count_card: &CountCard<N>, opts: &STVOptions) -> bool {
+	if let Some(vre) = &state.vote_required_election {
+		if opts.quota_mode == QuotaMode::ERS97 || opts.quota_mode == QuotaMode::ERS76 {
+			// VRE is set because ERS97/ERS76 rules
+			return cmp_quota_criterion(vre, count_card, opts);
+		} else {
+			// VRE is set because early bulk election is enabled and 1 vacancy remains
+			return count_card.votes > *vre;
+		}
+	} else {
+		return cmp_quota_criterion(state.quota.as_ref().unwrap(), count_card, opts);
+	}
+}
+
 /// Declare elected all candidates meeting the quota
 fn elect_meeting_quota<'a, N: Number>(state: &mut CountState<'a, N>, opts: &STVOptions) -> Result<bool, STVError> {
-	let vote_req = state.vote_required_election.as_ref().unwrap().clone(); // Have to do this or else the borrow checker gets confused
-	
 	let mut cands_meeting_quota: Vec<(&Candidate, &CountCard<N>)> = state.election.candidates.iter() // Present in order in case of tie
 		.map(|c| (c, &state.candidates[c]))
-		.filter(|(_, cc)| { (cc.state == CandidateState::Hopeful || cc.state == CandidateState::Guarded) && meets_quota(&vote_req, cc, opts) })
+		.filter(|(_, cc)| { (cc.state == CandidateState::Hopeful || cc.state == CandidateState::Guarded) && meets_vre(state, cc, opts) })
 		.collect();
 	
 	// Sort by votes
@@ -795,7 +806,7 @@ fn elect_meeting_quota<'a, N: Number>(state: &mut CountState<'a, N>, opts: &STVO
 		count_card.state = CandidateState::Elected;
 		state.num_elected += 1;
 		count_card.order_elected = state.num_elected as isize;
-		if meets_quota(state.quota.as_ref().unwrap(), count_card, opts) {
+		if cmp_quota_criterion(state.quota.as_ref().unwrap(), count_card, opts) {
 			// Elected with a quota
 			state.logger.log_smart(
 				"{} meets the quota and is elected.",
@@ -815,7 +826,7 @@ fn elect_meeting_quota<'a, N: Number>(state: &mut CountState<'a, N>, opts: &STVO
 			// Recheck as some candidates may have been doomed
 			let mut cmq: Vec<(&Candidate, &CountCard<N>)> = state.election.candidates.iter() // Present in order in case of tie
 				.map(|c| (c, &state.candidates[c]))
-				.filter(|(_, cc)| { (cc.state == CandidateState::Hopeful || cc.state == CandidateState::Guarded) && meets_quota(&vote_req, cc, opts) })
+				.filter(|(_, cc)| { (cc.state == CandidateState::Hopeful || cc.state == CandidateState::Guarded) && meets_vre(state, cc, opts) })
 				.collect();
 			cmq.sort_unstable_by(|a, b| a.1.votes.cmp(&b.1.votes));
 			cands_meeting_quota = cmq.iter().map(|(c, _)| *c).collect();

src/stv/wasm.rs

@@ -287,7 +287,8 @@ fn describe_count<N: Number>(filename: String, election: &Election<N>, opts: &st
 
 #[inline]
 fn should_show_vre(opts: &stv::STVOptions) -> bool {
-	return opts.quota_mode == stv::QuotaMode::ERS97 || opts.quota_mode == stv::QuotaMode::ERS76 || opts.early_bulk_elect;
+	//return opts.quota_mode == stv::QuotaMode::ERS97 || opts.quota_mode == stv::QuotaMode::ERS76 || opts.early_bulk_elect;
+	return opts.quota_mode == stv::QuotaMode::ERS97 || opts.quota_mode == stv::QuotaMode::ERS76;
 }
 
 /// Generate the first column of the HTML results table
@@ -360,7 +361,11 @@ fn update_results_table<N: Number>(stage_num: usize, state: &CountState<N>, opts
 	
 	result.push(&format!(r#"<td class="{}count">{}</td>"#, tdclasses2, pp(state.quota.as_ref().unwrap(), opts.pp_decimals)).into());
 	if should_show_vre(opts) {
-		result.push(&format!(r#"<td class="{}count">{}</td>"#, tdclasses2, pp(state.vote_required_election.as_ref().unwrap(), opts.pp_decimals)).into());
+		if let Some(vre) = &state.vote_required_election {
+			result.push(&format!(r#"<td class="{}count">{}</td>"#, tdclasses2, pp(vre, opts.pp_decimals)).into());
+		} else {
+			result.push(&format!(r#"<td class="{}count"></td>"#, tdclasses2).into());
+		}
 	}
 	
 	return result;

tests/utils/mod.rs

@@ -118,7 +118,8 @@ where
 				&"lbf" => approx_eq(&state.loss_fraction.votes, &votes, cmp_dps, idx, "LBF"),
 				&"nt" => approx_eq(&(&state.exhausted.votes + &state.loss_fraction.votes), &votes, cmp_dps, idx, "NTs"),
 				&"quota" => approx_eq(state.quota.as_ref().unwrap(), &votes, cmp_dps, idx, "quota"),
-				&"vre" => approx_eq(state.vote_required_election.as_ref().unwrap(), &votes, cmp_dps, idx, "VRE"),
+				//&"vre" => approx_eq(state.vote_required_election.as_ref().unwrap(), &votes, cmp_dps, idx, "VRE"),
+				&"vre" => approx_eq(state.vote_required_election.as_ref().unwrap(), &votes, Some(2), idx, "VRE"),
 				_ => panic!("Unknown sum_rows"),
 			}
 		}