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This paper presents a probabilistic perspective on iterative methods for approximating the solution x in R^d of a nonsingular linear system Ax = b. Classically, an iterative method produces a sequence x_m of approximations that converge to x in R^d. Our approach, instead, lifts a standard iterative method to act on the set of probability distributions, P(Rd), outputting a sequence of probability distributions  mu_m in P(Rd). The output of a probabilistic iterative method can provide both a “best guess” for x, for example by taking the mean of  mu_m, and also probabilistic uncertainty quantification for the value of x when it has not been exactly determined. A comprehensive theoretical treatment is presented in the case of a stationary linear iterative method, where we characterise both the rate of contraction of  mu_m to an atomic measure on x and the nature of the uncertainty quantification being provided. We conclude with an empirical illustration that highlights the potential for probabilistic iterative methods to provide insight into solution uncertainty. 

This paper presents a probabilistic perspective on iterative methods for approximating the solution x in R^d of a nonsingular linear system Ax = b. Classically, an iterative method produces a sequence x_m of approximations that converge to x in R^d. Our approach, instead, lifts a standard iterative method to act on the set of probability distributions, P(Rd), outputting a sequence of probability distributions  mu_m in P(Rd). The output of a probabilistic iterative method can provide both a “best guess” for x, for example by taking the mean of mu_m, and also probabilistic uncertainty quantification for the value of x when it has not been exactly determined. A comprehensive theoretical treatment is presented in the case of a stationary linear iterative method, where we characterise both the rate of contraction of  mu_m to an atomic measure on x and the nature of the uncertainty quantification being provided. We conclude with an empirical illustration that highlights the potential for probabilistic iterative methods to provide insight into solution uncertainty.