The degrees of freedom of the Lasso in underdetermined linear regression models
Abstract
In this paper, we investigate the degrees of freedom (df) of penalized l1 minimization (also known as the Lasso) for an un-derdetermined linear regression model. We show that under a suitable condition on the design matrix, the number of nonzero coefficients of the Lasso solution is an unbiased estimate for the degrees of freedom. An effective estimator of the number of degrees of freedom may have several applications including an objectively guided choice of the regularization parameter in the Lasso through the SURE or GCV frameworks.
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