resemble (version 3.0.1)

mbl_control: Control parameters for memory-based learning

Description

This function controls various aspects of the memory-based learning process in the mbl function.

Usage

mbl_control(
  return_dissimilarity = FALSE,
  validation_type = "NNv",
  tune_locally = TRUE,
  number = 10,
  p = 0.75,
  range_prediction_limits = TRUE,
  allow_parallel = TRUE,
  blas_threads = 1L
)

Value

A list of class mbl_control with the specified control parameters.

Arguments

return_dissimilarity

Logical indicating whether to return the dissimilarity matrix between Xr and Xu. Default is FALSE.

validation_type

Character vector specifying validation method(s):

• "NNv": Leave-nearest-neighbor-out cross-validation (default, faster)

• "local_cv": Local leave-group-out cross-validation

• "none": No validation

Multiple methods can be specified (e.g., c("NNv", "local_cv")). Default is "NNv".

tune_locally

Logical indicating whether to tune PLS components locally when validation_type = "local_cv" and using fit_pls or fit_wapls. Default is TRUE.

number

Integer specifying the number of sampling iterations for "local_cv" validation. Default is 10.

p

Numeric value between 0 and 1 indicating the proportion of observations retained at each "local_cv" iteration. Default is 0.75.

range_prediction_limits

Logical indicating whether predictions should be constrained to the range of response values in each neighborhood. Default is TRUE.

allow_parallel

Logical indicating whether parallel execution is allowed via the foreach package. Default is TRUE.

blas_threads

Integer specifying the number of BLAS threads to use during mbl() execution. Default is 1L, which avoids thread overhead from repeated small matrix operations. Requires the RhpcBLASctl package to take effect. The original thread count is restored after mbl() completes. See Details.

Author

Leonardo Ramirez-Lopez and Antoine Stevens

Details

Validation methods

Leave-nearest-neighbor-out cross-validation ("NNv"): For each target observation, the nearest neighbor is excluded from the local model, which then predicts that neighbor's value. This is faster than "local_cv". If the nearest neighbor belongs to a group (specified via the group argument in mbl), all group members are excluded.

Local leave-group-out cross-validation ("local_cv"): The neighborhood is partitioned into subsets via stratified random sampling. Each subset serves as validation data while the remainder fits the model. This repeats number times, with p controlling the training proportion. The final error is the average local RMSE.

BLAS threading

On Linux systems with multi-threaded OpenBLAS, the default thread count can cause significant overhead for algorithms like mbl() that perform many small matrix operations. Setting blas_threads = 1 (the default) eliminates this overhead.

This setting requires the RhpcBLASctl package. If not installed, the parameter is ignored and a message is displayed. The original thread count is restored when mbl() completes.

Windows systems typically use single-threaded BLAS by default, so this setting has no effect there.

References

Ramirez-Lopez, L., Behrens, T., Schmidt, K., Stevens, A., Dematte, J.A.M., Scholten, T. 2013a. The spectrum-based learner: A new local approach for modeling soil vis-NIR spectra of complex data sets. Geoderma 195-196:268-279.

Ramirez-Lopez, L., Behrens, T., Schmidt, K., Viscarra Rossel, R., Dematte, J.A.M., Scholten, T. 2013b. Distance and similarity-search metrics for use with soil vis-NIR spectra. Geoderma 199:43-53.

See Also

mbl, neighbors_k, neighbors_diss

Examples

# Default control parameters (NNv validation)
mbl_control()

# Both validation methods
mbl_control(validation_type = c("NNv", "local_cv"))

# No validation
mbl_control(validation_type = "none")

# NNv validation only, no parallel
mbl_control(validation_type = "NNv", allow_parallel = FALSE)

# Allow more BLAS threads (if needed for other computations)
mbl_control(blas_threads = 4)