We develop nearly-linear time algorithms for approximately solving sparse symmetric diagonally-dominant linear systems. In particular, we present a linear-system solver that, given an n-by-n symmetric diagonally-dominant matrix A with m non-zero entries and an n-vector b, produces a vector x̃ satisfying ‖x̃ − x‖A ≤ ǫ, where x is the solution to Ax = b, in time m log m+O (m log(1/ǫ)) + n2 √ log n ...