Here, N is the number of rows of the detection matrix, x is a binary vector of length N and x i = 1 if the ith row of the detection matrix is selected; f is the detection coverage and ∥x∥ 1 is the L 1 norm of the binary vector which is the number of selected rows. Note that for solutions which unduly exceed the budget (by two times in this setting), the corresponding objective value in g 1 is set to be negative infinity to make the subsequent searching process more efficient.