symbols is related to the number of levels per variable in the sample
set (a larger number of symbols equates to more stratification and
fewer replications). For example, if symbols = 7, each variable would be
divided into seven levels.
Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA-0003525.