Notes from a Medium-Sized Island

Oh god I gave Delta my email address so's they could send me flight updates and they sent me a heartbreakingly standard, cheerful "okay then! let's get ready for your flight tomorrow!" email. And they haven't cancelled my flight yet.

"Heartbreakingly" because I just can't believe it it's going to happen, given the news. Current state of affairs seems to be airlines making a few test flights, and saying they they might resume flights in a week. Are the journalists overreacting? Am I misinterpreting? Am I reading into UK news too much, where the ash cloud is denser? I dare say I suspect I'll be flying over UK airspace on the way back to the US, given the way great circles work out and such.

Here's a cute little decision-theoretic puzzle that I fished out of a book:

Suppose you have a starting blob of money, say X dollars. Each day, you choose how to divide your money between consumption and investment. If you consume Y dollars, then you get ln(Y) utility out of that act of consumption. If you invest Z dollars, (really, Z = X - Y; any money you don't spend automatically gets "invested") then you get back R*Z dollars on the next day, where R is a number given to you by the universe, indicating the return you can manage to get on investments. Finally, we make the assumption that you're impatient: the actual value of you today of a util earned far in the future, say on day T, is really only D^T, where D is some "discounting factor", a number less than (but perhaps quite close to) one.

Given that, what strategy optimizes the sum of the present values of all future rewards?

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Ok, so my flight tomorrow has been canceled and rescheduled to... the same flight tomorrow? I called Delta and got a busy tone, and emailed 'em after that.