Quote from: asher2 on August 30, 2011, 04:33:23 AM

Allowing users to change the N value themselves is a terrible idea for pool operators. Anyone implementing this please let me know though Cheesy

It won't be too bad if some limitations are imposed, e.g. X must be between 0.1 and 10, and can be changed only once per day. I want to say "and only after the account has already submitted some number of shares", but that may be too inconvenient for honest newcomers.

Quote from: c_k on August 30, 2011, 05:10:39 AM

Quote from: Meni Rosenfeld on August 28, 2011, 12:04:16 PM

However, if implemented incorrectly, it is possible to hop based on imminent difficulty changes.

I wonder what the real world implications of this are - roughly: A 10 GH/s user that has an expected reward of 10 BTC can get an extra 0.2 BTC based on the difficulty decreasing 2% ?

Basically yes. If N is a fixed number of shares, D1 is the current difficulty, D2 is the future difficulty, p1=1/D1 and p2=1/D2, then the expectation for a share submitted just before the difficulty change is p2B where the fair reward is p1B, an increase by a factor of D1/D2. For a share submitted N shares before the difficulty change, the fair reward p1B is obtained. For the in-between period it increases linearly from p1B to p2B, so the total extra that could be obtained (with enough hashrate) is (p2-p1)NB/2 per difficulty change. Of course, to exploit it will require a reasonably accurate estimate of the time of difficulty adjustment, which is easier to do if the hashrate of the pool (including hoppers) is small.