tweak_initial_estimates: Tweak the initial parameter estimates

In metrumresearchgroup/rbabylon: R package for bbi

Tweak the initial parameter estimates

Description

Tweak the initial parameter estimates

Usage

tweak_initial_estimates(.mod, .p = 0.1, tweak = c("theta"), digits = 3)

Arguments

.mod	model object to update.
.p	Percent to tweak the initial parameter estimates by. Represented as a decimal.
tweak	type of estimates to tweak in the model. Only "theta" is currently supported, though "omega" and "sigma" will be options at a later date.
digits	Number of significant digits to round estimates to.

Details

In the following cases, the initial estimate will not be updated:

• Individual FIXED THETA parameters

  • e.g., ⁠$THETA 1.2 FIX 1.5 0.2⁠ –> would only skip the first value

• THETA parameters with no initial estimate

  • e.g., ⁠$THETA (0,,1)⁠

For bounded THETA estimates:

• If an initial THETA has bounds and an initial estimate (e.g., ⁠(0, 0.5, 1)⁠, ⁠(0,1)⁠), the bounds will be respected when sampling a percent to tweak by. If the tweaked value would fall below the lower bound, the initial estimate will be set to 90% of the way between the initial value and lower bound. If after rounding, the value would still not be within the bounds, the difference between the initial value and the bound will be iteratively reduced until it is. The same is true for upper bounds.

  • e.g., ⁠(0, 0.5, 1)⁠ –> tweak initially, falls outside bound (⁠(0, 1.2, 1)⁠) –> set to value within bounds (first iteration: 0.5 + (1-0.5)*0.9: (⁠(0, 0.95, 1)⁠)

Examples

## Not run: 
base_mod <- read_model(file.path(MODEL_DIR, "1"))

mod2 <- copy_model_from(base_mod, "mod2") %>%
  tweak_initial_estimates(.p = 0.2)

# This function may be paired with `inherit_param_estimates()`:
mod2 <- copy_model_from(base_mod, "mod2") %>%
  inherit_param_estimates() %>% tweak_initial_estimates(.p = 0.2)

# If you want to set the seed for reproducible results:
mod2 <- withr::with_seed(1234, {
   tweak_initial_estimates(mod2, .p = 0.2, digits = 3)
})


## End(Not run)

metrumresearchgroup/rbabylon documentation built on April 21, 2024, 3:26 a.m.