# pen_function: Elastic net penalty value

## Description

Returns the elastic net penalty value without the `lambda`

factor.

## Usage

pen_function(coefficients, alpha = 1, vp = 1)

## Arguments

coefficients

The model's coefficients (excluding intercept).

alpha

The elasticnet mixing parameter, with \(0 \le \alpha \le 1\).

vp

Penalty factors for each of the coefficients.

## Details

The penalty is defined as
$$(1-\alpha)/2 \sum vp_j \beta_j^2 + \alpha \sum vp_j |\beta|.$$
Note the omission of the multiplicative `lambda`

factor.