Better prime election.

frame/elections-phragmen/src/lib.rs

@@ -971,19 +971,26 @@ impl<T: Trait> Module<T> {
 			// save the members, sorted based on account id.
 			new_members.sort_by(|i, j| i.0.cmp(&j.0));
 
+			// Now we select a prime member using a [Borda count](https://en.wikipedia.org/wiki/Borda_count).
+			// We weigh everyone's vote for that new member by a multiplier based on the order
+			// of the votes. i.e. the first person a voter votes for gets a 16x multiplier,
+			// the next person gets a 15x multiplier, an so on... (assuming `MAXIMUM_VOTE` = 16)
 			let mut prime_votes: Vec<_> = new_members.iter().map(|c| (&c.0, BalanceOf::<T>::zero())).collect();
 			for (_, stake, targets) in voters_and_stakes.into_iter() {
-				for (votes, who) in targets.iter()
+				for (vote_multiplier, who) in targets.iter()
 					.enumerate()
-					.map(|(votes, who)| ((MAXIMUM_VOTE - votes) as u32, who))
+					.map(|(vote_position, who)| ((MAXIMUM_VOTE - vote_position) as u32, who))
 				{
 					if let Ok(i) = prime_votes.binary_search_by_key(&who, |k| k.0) {
 						prime_votes[i].1 = prime_votes[i].1.saturating_add(
-							stake.saturating_mul(votes.into())
+							stake.saturating_mul(vote_multiplier.into())
 						);
 					}
 				}
 			}
+			// We then select the new member with the highest weighted stake. In the case of
+			// a tie, the last person in the list with the tied score is selected. This is
+			// the person with the "highest" account id based on the sort above.
 			let prime = prime_votes.into_iter().max_by_key(|x| x.1).map(|x| x.0.clone());
 
 			// new_members_ids is sorted by account id.