“…To remedy this problem, many nonconvex sparse recovery methods have been employed to better approximate the ℓ 0 -norm and enhance sparsity. They include ℓ p (0 < p < 1) [10][11][12], smoothed L0 (SL0) [13], Capped-L1 [14], transformed ℓ 1 (TL1) [15], smooth clipped absolute deviation (SCAD) [9], minimax concave penalty (MCP) [16], nonconvex shrinkage methods, [17], exponential-type penalty (ETP) [18,19], error function (ERF) method [20], ℓ 1 − ℓ 2 [21,22], ℓ r r − αℓ r 1 (α ∈ [0, 1], r ∈ (0, 1]) [23], ℓ 1 /ℓ 2 [24,25], q-ratio sparsity minimization [26] and smoothed ℓ p -over-ℓ q (SPOQ) [27], among others. For a more comprehensive view, please see the survey on nonconvex regularization [28] and the references therein.…”