trop_threads() gives the default number of threads for trop_control().
Value
An integer. If the option fasttrop.threads has a value, the
function returns this value. If not, the function returns the number of
physical cores, with a minimum of 1. When the environment variable
_R_CHECK_LIMIT_CORES_ has a value other than "false", the maximum is 2.
R CMD check --as-cran sets this variable.