### Purpose

Parameter estimation with Monolix and simulation with Simulx or Mlxplore are different tasks. Because of this there are some differences in what sections and blocks need to be included in a Mlxtran model used for parameter estimation with Monolix compared to a Mlxtran model used for simulation with Simulx or Mlxplore.

### Mlxplore: model exploration for continuous models

The purpose of Mlxplore is the exploration and visualization of models. Mlxplore is used to study the model prediction and the inter-individual variability. The observational model (error model) is not included in Mlxplore. Because of this only continuous data models can be simulated.

### Monolix: parameter estimation for non-linear mixed effect models

The purpose of Monolix is the parameter estimation in non linear mixed effects models. Monolix provides a user interface to define the statistical elements of the models. Therefore, some of the sections and blocks are not needed. For continuous data models the observational must not be defined in the Mlxtran file. The individual model and the covariate model must not be defined in the Mlxtran file. This means the following rules apply for all Mlxtran model for Monolix:

- Except regressors, the input parameters of [LONGITIDINAL] are only the outputs of [INDIVIDUAL] and eventually parameters of the error models (if used)
- The entire [INDIVIDUAL] section is never used
- The entire [COVARIATE] section is never used

### Simulx: clinical trial simulation

The purpose of Simulx are simulations for any non linear mixed effects models. In contrast to Mlxplore, Simulx can also be used with an observational model (error model).