All of Daniel Munro's Comments + Replies

Fascinating. But are these diagrams really showing HMMs? I thought each state in an HMM had a set of transition probabilities and another set of emission probabilities, which at each step are sampled independently. In these diagrams, the two processes are coupled. If "Even Ys" were a conventional HMM,  would sometimes emit X and transition to , which would result in some even and some odd runs of Y. Are these a special variant of HMM, or some other type of state machine? And would these results apply to conventional HMMs with separate tr... (read more)

It seems to me that Rule 1 is a direct translation of the Sleeping Beauty problem into a betting strategy question, while the other rules correspond to different questions where a single outcome depends on some function of the two guesses in the case of tails. Doing the experiment 100 times under that rule, Beauty will have around 150 identical awakening experiences. The payout for each correct guess is the same, $1, and the correct guess would be tails 2/3 of the time. So surely the probability that the coin had landed tails prior to these events is 2/3? ... (read more)

1Ape in the coat
There is no such thing as direct translation of a problem into a betting strategy question. A model for a problem should be able to deal with any betting schemes, no matter how extravagant. And the scheme where the Beauty can bet on every awakening is quite extravagant. It's an asymetric bet on a coin toss, where Tails outcome is rewarded twice as Heads outcome. If there is no information update then the probability of the coin to be Tails can't change from 1/2 to 2/3. It would contradict the law of conservation of expected evidence. As I've written in the Effects of Amnesia section, from Beauty's perspective Tails&Monday and Tails&Tuesday awakening are still part of the same elementary outcome because she remembers the setting of the experiment. If she didn't know that Tails&Monday and Tails&Tuesday necessary follow each other, if all she knew is that there are three states in which she can awaken, then yes, she should've reasoned that P(Tails)=2/3. Alternatively if the question was about a random awakening of the Beauty among multiple possible experiments, then, once again, P(Heads) would be 1/3. But in the experiment as stated, the Beauty isn't experiencing a random awakening, she is experiencing ordered awakening, determined by a coin toss.