We examine a Markovian model for the price evolution of a stock, in which the probability of local upward or downward movement is arbitrarily dependent on the current price itself (and perhaps some auxiliary state information). Our main result is a “universally profitable” trading strategy — a single fixed strategy whose profitability competes with the optimal strategy, which knows all of the underlying parameters of the infinite and possibly nonstationary Markov process.
Sham M. Kakade, Michael J. Kearns