CV_core contains the core parts of the cross-validation for Lasso and Post-Lasso.
CV_core(x, y, w, cvgroup, list, i, lambda, ...)MSE_lasso / MSE_plasso: means squared errors for each lambda.
Covariate matrix to be used in cross-validation
Vector of outcomes
Vector of weight
Categorical with k groups to identify folds
List 1:k
Number of fold that is used for prediction
Series of lambdas used
Pass glmnet options