Object for elastic net optimization with ista optimizer
a list with fit results
newcreates a new object. Requires (1) a vector with weights for each parameter, (2) a vector indicating which penalty is used, and (3) a list with control elements
optimizeoptimize the model. Expects a vector with starting values, a SEM of type SEM_Cpp, a theta value, a lambda and an alpha value (alpha must be 1).