A sensible metalearner based on Lrnr_solnp is chosen based on
outcome type. This amounts to choosing an appropriate loss function and
combination function.
default_metalearner(outcome_type)a Variable_Type object
| Outcome Type | Combination Function | Loss Function |
| binomial | metalearner_logistic_binomial | loss_squared_error |
| categorical | metalearner_linear_multinomial | loss_loglik_multinomial |
| continuous | metalearner_linear | loss_squared_error |
| multivariate | metalearner_linear_multivariate | loss_squared_error_multivariate |