`glmnet::glmnet()`

fits a model that uses linear predictors to predict
multiclass data using the multinomial distribution.

## Details

For this engine, there is a single mode: classification

### Tuning Parameters

This model has 2 tuning parameters:

`penalty`

: Amount of Regularization (type: double, default: see
below)

`mixture`

: Proportion of Lasso Penalty (type: double, default: 1.0)

A value of `mixture = 1`

corresponds to a pure lasso model, while
`mixture = 0`

indicates ridge regression.

The `penalty`

parameter has no default and requires a single numeric
value. For more details about this, and the `glmnet`

model in general,
see glmnet-details.

### Translation from parsnip to the original package

## Multinomial Regression Model Specification (classification)
##
## Main Arguments:
## penalty = 0
## mixture = double(1)
##
## Computational engine: glmnet
##
## Model fit template:
## glmnet::glmnet(x = missing_arg(), y = missing_arg(), weights = missing_arg(),
## alpha = double(1), family = "multinomial")

### Preprocessing requirements

Factor/categorical predictors need to be converted to numeric values
(e.g., dummy or indicator variables) for this engine. When using the
formula method via
`fit.model_spec()`

, parsnip will
convert factor columns to indicators.

Predictors should have the same scale. One way to achieve this is to
center and scale each so that each predictor has mean zero and a
variance of one. By default, `glmnet::glmnet()`

uses
the argument `standardize = TRUE`

to center and scale the data.

### Examples

The “Fitting and Predicting with parsnip” article contains
examples
for `multinom_reg()`

with the `"glmnet"`

engine.

### References

Hastie, T, R Tibshirani, and M Wainwright. 2015. *Statistical
Learning with Sparsity*. CRC Press.

Kuhn, M, and K Johnson. 2013. *Applied Predictive Modeling*.
Springer.