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A general description is here.
Matrix products now consistently bypass BLAS when the inputs have NaN/Inf values. Performance of the check of inputs has been improved. Performance when BLAS is used is improved for matrix/vector and vector/matrix multiplication (DGEMV is now used instead of DGEMM).
One can now choose from alternative matrix product implementations via ‘options(matprod = )’. The ‘"internal"’ implementation is unoptimized but consistent in precision with other summation in R (uses ‘long double’ accumulators). ‘"blas"’ calls BLAS directly for best performance, yet usually with undefined behavior for inputs with NaN/Inf.
Improved performance and robustness of matrix multiplication using
BLAS: DGEMV is now used instead of DGEMM for matrix/vector and
vector/matrix multiplication, ZGEMM/DGEMM/DGEMV is bypassed when the
input has NaN or Inf values, and performance for these input checks has
been improved.
If available, the POSIX 2008 system call ‘utimensat’ will be used by ‘Sys.setFileTime()’ and ‘file.copy(copy.date = TRUE)’. This may result in slightly more accurate file times. (It is available on Linux and FreeBSD but not macOS nor Solaris.)