“…FOCUSS, which stands for FOCal Underdetermined System Solver, is an algorithm designed to obtain suboptimally (and, at times, maximally) sparse solutions to the following m × n, underdetermined linear inverse problem 1 (Gorodnitsky, George, & Rao, 1995;Adler, Rao, & Kreutz-Delgado, 1996;Rao, 1997Rao, ,1998, (1.1) for known A. The sparsity of a vector is the number of zero-valued elements (Donoho, 1994), and is related to the diversity, the number of nonzero elements, Since our initial investigations into the properties of FOCUSS as an algorithm for providing sparse solutions to linear inverse problems in relatively noise-free environments (Gorodnitsky et al, 1995;Rao, 1997;Adler et al, 1996;, we now better understand the behavior of FOCUSS in noisy environments and as an interior point-like optimization algorithm for optimizing concave functionals subject to linear constraints , 1998c, 1999KreutzDelgado, Rao, Engan, Lee, & Sejnowski, 1999a;Engan, Rao, & Kreutz-Delgado, 2000;Rao, Engan, Cotter, & Kreutz-Delgado, 2002).…”