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  • Stochastic Approximation fo...
    Huang, Wenjie; Haskell, William B.

    IEEE transactions on automatic control, 03/2021, Letnik: 66, Številka: 3
    Journal Article

    We develop a stochastic approximation-type algorithm to solve finite state/action, infinite-horizon, risk-aware Markov decision processes. Our algorithm has two loops. The inner loop computes the risk by solving a stochastic saddle-point problem. The outer loop performs <inline-formula><tex-math notation="LaTeX">Q-</tex-math></inline-formula> learning to compute an optimal risk-aware policy. Several widely investigated risk measures (e.g., conditional value-at-risk, optimized certainty equivalent, and absolute semideviation) are covered by our algorithm. Almost sure convergence and the convergence rate of the algorithm are established. For an error tolerance <inline-formula><tex-math notation="LaTeX">\epsilon >0</tex-math></inline-formula> for optimal <inline-formula><tex-math notation="LaTeX">Q</tex-math></inline-formula>-value estimation gap and learning rate <inline-formula><tex-math notation="LaTeX">k\in (1/2,\,1</tex-math></inline-formula>, the overall convergence rate of our algorithm is <inline-formula><tex-math notation="LaTeX">\Omega ((\ln (1/\delta \epsilon)/\epsilon ^{2})^{1/k}+(\ln (1/\epsilon))^{1/(1-k)})</tex-math></inline-formula> with probability at least <inline-formula><tex-math notation="LaTeX">1-\delta</tex-math></inline-formula>.