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© 2020 Masaaki Nagahara
In the previous chapter, we have formulated the problem of sparse representation as optimization problems with ℓ1 norm, for which there are efficient and fast algorithms. The idea was to approximate the non-convex and discontinuous ℓ0 norm by the convex ℓ1 norm. In this chapter, we consider alternative algorithms that directly solve the ℓ0-norm optimization by using the greedy method.