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Jul 26, 2022 at 19:52 comment added littleO We can use the KKT conditions (Lagrange multiplier optimality conditions) from convex optimization to show that a minimizer for problem 2 (which has a hard constraint) is also a minimizer for problem 1, for a certain value of $\lambda$. The parameter $\lambda$ is a Lagrange multiplier.
Jul 21, 2022 at 13:21 comment added Stephan Kolassa I don't think it's of much interest in itself. If you look at the original Tibshirani (1996) paper, the lasso is actually introduced by an analogue of equation (6.8), and this of course motivates the term "lasso": the coefficients are constrained in a hard way (through their 1-norm), not in a soft way (per 6.7, where coefficient size can be traded off against model fit). I think the (nowadays more common) formulation (6.7) simply came later.
Jul 21, 2022 at 13:10 comment added Dan Thank you for your reply! I do have one question however. In answer no 1, you said, "for every 𝜆, there is one 𝑠 such that the minimizer 𝛽 of (6.7) for 𝜆 is equal to the minimizer of (6.8)". Why is that particular s value of interest?
Jul 21, 2022 at 12:10 vote accept Dan
Jul 21, 2022 at 10:07 history edited Stephan Kolassa CC BY-SA 4.0
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Jul 21, 2022 at 7:48 history answered Stephan Kolassa CC BY-SA 4.0