multicool

Changes in behaviour

• initMC() now gives an error, rather than a warning, for input with fewer than two elements, and an error for input containing missing values.
• initMC() keeps the type of its input, so logical multisets are permuted as logicals rather than as the strings "TRUE" and "FALSE".

Bug fixes

• initMC() with non-whole numbers (e.g. c(1.5, 1.5, 2.5)) permuted the counts of each value rather than the values themselves.
• Stirling2() and Bell() overflowed for moderate arguments, and much sooner on Windows (e.g. Stirling2(20, 5) and Bell(16) were wrong).
• multinom() overflowed silently for large coefficients.
• genComp() crashed R when n was zero or negative, and returned NULL when len was greater than n.
• Calling allPerm() no longer resets the position of nextPerm().
• Fixed a memory leak in the permutation object.

Improvements

• genComp() is much faster for larger n. The time taken previously grew quadratically with the number of partitions (about 100 seconds for n = 50).
• allPerm() is 10 to 30 times faster and uses much less memory. It writes the elements straight into the result matrix in C++. In the permutation benchmarks from <https://stackoverflow.com/questions/22569176>, it now takes 1.4 to 1.9 times as long as single-threaded 'RcppAlgos' (before, 15 to 54 times as long), and 1.0 to 1.5 times as long as 'arrangements'.
• initMC() keeps integer input as integer, so allPerm() returns an integer matrix for integer input.
• nextPerm() is about 9 times faster per call (about 0.9 rather than 8.4 microseconds), because the permutation object is now reached through an external pointer rather than an Rcpp Module.
• nextPerm() checks that its argument is an mc object.
• Using an mc object after it has been saved and reloaded gives a clear error asking you to call initMC() again.
• Native routines are now registered, and documentation and NAMESPACE are generated with roxygen2.

Acknowledgements

• Earlier versions of this package used C++ code by Dave Barber (<http://tamivox.org/dave/multinomial/code.html>) to compute multinomial coefficients. It has been replaced by exact computation with the 'gmp' package, but we thank Dave for the code that the package relied on for many years.