There can be ties at any point during the iterative elimination process, not just during the final round (if anything they are more likely in earlier rounds).
From the link above:
For small IRV elections, there can be frequent last-place ties that prevent clear bottom elimination, so it’s critically important to have a clear tie-breaking mechanism in jurisdictions with few voters.
Ah, I hadn’t thought of that, and I can see how this makes the results indeterminate (because reallocating the votes from one joint-last candidate could bump the other joint-last candidate up from the bottom).
I’ll have a think about how to handle this and get back to you, my initial thought is still to break ties randomly (with a stable-but-random ranking of the precedence of each candidate in a tie).
There can be ties at any point during the iterative elimination process, not just during the final round (if anything they are more likely in earlier rounds).
From the link above:
Ah, I hadn’t thought of that, and I can see how this makes the results indeterminate (because reallocating the votes from one joint-last candidate could bump the other joint-last candidate up from the bottom).
I’ll have a think about how to handle this and get back to you, my initial thought is still to break ties randomly (with a stable-but-random ranking of the precedence of each candidate in a tie).