This function studies the change in permformance as the sizes of the training
set is varied. In case the studied modeling procedures cannot
produce models on the smallest training sets, please use
.return_error=TRUE (see evaluate.
Fraction of dataset to hold out, i.e. use as test set. Defaults
20 logarithmically distributed values ranging from all but 5 observations
per class in the largest test set to only 5 observations per class in
the smallest test set.