“…where c 0 = {the number of indices k such that c k = 0} measures the sparsity of c. In (6), δ is a tolerance of solution inaccuracy due to the truncation of the expansion. While, the problem (6) is NP-hard to solve, approximate solutions may be obtained in polynomial time using a variety of greedy algorithms including orthogonal matching pursuit (OMP) [29,30,31,32], compressive sampling matching pursuit (CoSaMP) [33,34], and subspace pursuit (SP) [35], or convex relaxation via ℓ 1 -minimization [5,6]. The key advantage of an approximation via compressed sensing is that, if the QoI is approximately sparse, stable and convergent approximations of c can be obtained using N < P random samples of u(Ξ), as long as Φ satisfies certain conditions [5,6,10,36,21,27].…”