liblex_control: Control parameters for liblex

In resemble: Similarity Retrieval and Local Learning for Spectral Chemometrics

Control parameters for liblex

Description

Specifies control parameters for the liblex function, including output options, validation settings, tuning behavior, and parallel execution.

Usage

liblex_control(
  return_dissimilarity = FALSE,
  mode = c("build", "validate"),
  tune = FALSE,
  metric = c("rmse", "r2"),
  chunk_size = 1L,
  allow_parallel = TRUE,
  blas_threads = 1L
)

Arguments

return_dissimilarity	A logical indicating whether the dissimilarity matrix should be returned in the output. Default is FALSE. Setting to TRUE can be useful for diagnostics but increases memory usage for large libraries.
mode	A character string specifying the operation mode: "build" (default) Builds the library of local models. If tune = TRUE, validation is performed first to find optimal parameters, then the library is built using those parameters. If tune = FALSE, the library is built directly using the parameters provided to liblex. "validate" Performs validation only without building the library. Useful for parameter exploration or when testing different configurations before committing to the full library build.
tune	A logical indicating whether to optimize parameters via nearest-neighbor validation. Default is FALSE. When TRUE, the function evaluates all combinations of k values and PLS component ranges, selecting the combination that minimizes RMSE (or maximizes R², depending on metric). See Details.
metric	A character string specifying the performance metric used for parameter selection when tune = TRUE. Options are: "rmse" (default) Root mean squared error (minimized). "r2" Coefficient of determination (maximized). Ignored when tune = FALSE.
chunk_size	An integer specifying the number of local models to process per parallel task. Default is 1L. Increasing this value reduces parallel overhead but may cause load imbalance. For large libraries, values between 10 and 50 often provide a good trade-off between overhead and efficiency.
allow_parallel	A logical indicating whether parallel execution is permitted. Default is TRUE. Parallelization is applied to the model fitting loop using the foreach package. Requires a registered parallel backend (e.g., via doParallel).
blas_threads	An integer specifying the number of threads for BLAS operations. Default is 1L, which avoids thread contention when using parallel processing. Requires the RhpcBLASctl package to take effect. On Linux systems with multi-threaded BLAS (e.g., OpenBLAS), setting this to 1 can substantially improve performance when allow_parallel = TRUE.

Details

Nearest-neighbor validation

When tune = TRUE or mode = "validate", the function performs nearest-neighbor validation (NNv) to assess model performance. For each observation in the reference set (or anchor set, if specified), the procedure:

1. Identifies the k nearest neighbors of the target observation.

2. Excludes the target observation (and any observations in the same group, if group is specified) from the neighbor set.

3. Fits a local model using the remaining neighbors.

4. Predicts the response value for the excluded target observation.

5. Computes prediction errors across all observations.

This leave-one-out style validation provides an estimate of prediction performance without requiring a separate test set. When tune = TRUE, the parameter combination (number of neighbors and PLS component range) yielding the best performance according to metric is selected for building the final library.

Mode and tune combinations

mode	tune	Behavior
"build"	FALSE	Build library using parameters as provided
"build"	TRUE	Validate, find optimal parameters, build library
"validate"	FALSE	Validate only, report performance statistics
"validate"	TRUE	Validate, report statistics with optimal parameters identified

Parallel chunk size

The chunk_size parameter controls granularity of parallel work distribution. When allow_parallel = TRUE and a parallel backend is registered:

• chunk_size = 1: Each local model is a separate parallel task. Maximum parallelism but higher scheduling overhead.

• chunk_size > 1: Multiple models are processed sequentially within each parallel task. Reduces overhead and improves memory locality, but may cause load imbalance if the number of models is not evenly divisible.

When allow_parallel = FALSE, chunk_size has no effect.

Value

A list of class liblex_control containing the validated control parameters.

Author(s)

Leonardo Ramirez-Lopez

See Also

liblex, mbl_control

Examples

# Default settings: build library without tuning
liblex_control()

# Tune parameters before building
liblex_control(tune = TRUE)

# Validate only for parameter exploration
liblex_control(mode = "validate", tune = TRUE)

# Include dissimilarity matrix in output
liblex_control(return_dissimilarity = TRUE)

# Larger chunks for reduced parallel overhead
liblex_control(chunk_size = 20L)

# Parallel settings for Linux with OpenBLAS
liblex_control(allow_parallel = TRUE, blas_threads = 1L)

resemble documentation built on April 21, 2026, 1:07 a.m.