Internal function that does the forward step for the stepwise function.
forward_step(empty_start_dataset, fit, data, formula,
interactive_mode = FALSE, genes_current = NULL, env_current = NULL,
genes_toadd = NULL, env_toadd = NULL, search = "genes",
search_criterion = "AIC", p_threshold = 0.2,
exclude_worse_AIC = TRUE, max_steps = 100, cv_iter = 5,
cv_folds = 10, folds = NULL, Huber_p = 1.345,
classification = FALSE, start_genes = NULL, start_env = NULL,
eps = 0.01, maxiter = 100, family = gaussian, ylim = NULL,
seed = NULL, print = TRUE)
If TRUE, the initial dataset is empty.
Current best fit.
Same parameters as in the stepwise function.
Returns fit, start_genes, start_env and genes_current, genes_toadd if search="genes" or env_current and env_toadd if search="env".