The null space property and the restricted isometry property for a measurement matrix are two basic properties in compressive sampling, and are closely related to the sparse approximation. In this paper, we introduce the sparse approximation property of order s for a measurement matrix A: ‖xs‖2 ≤ D‖Ax‖2 + β σs(x) √ s for all x, where xs is the best s-sparse approximation of the vector x in `, σ...