Simulation

The optional [simulation] block defines a virtual clinical trial design for generating simulated data. This is useful for model validation and testing.

Syntax

[simulation]
  subjects = N
  dose = AMOUNT
  cmt = COMPARTMENT
  seed = SEED
  times = [t1, t2, t3, ...]

Example

[simulation]
  subjects = 100
  dose = 100
  cmt = 1
  seed = 12345
  times = [0.5, 1, 2, 4, 8, 12, 24]

This simulates 100 subjects, each receiving a dose of 100 units into compartment 1, with observations at 0.5, 1, 2, 4, 8, 12, and 24 hours.

Usage

Run a simulation-estimation study from the CLI:

ferx model.ferx --simulate

This will:

1. Parse the model and [simulation] block
2. Generate simulated data using the model's default parameters and random effects
3. Fit the model to the simulated data
4. Report parameter estimates and diagnostics

Simulation Process

1. For each subject, random effects are sampled from \( \eta_i \sim N(0, \Omega) \)
2. Individual parameters are computed using the [individual_parameters] equations
3. Predictions are generated using the structural model
4. Residual error is added: \( DV = IPRED + \epsilon \), where \( \epsilon \sim N(0, V) \)
5. Observations below 0.001 are clipped to 0.001

Covariates in Simulation

Covariates can be specified per subject in the [simulation] block. Currently, the simulated population uses default covariate values (covariates are not randomized).