$ brew install openblas
==> Caveats
This formula is keg-only, which means it was not symlinked into /usr/local,
because macOS provides BLAS and LAPACK in the Accelerate framework.
For compilers to find this software you may need to set:
LDFLAGS: -L/usr/local/opt/openblas/lib
CPPFLAGS: -I/usr/local/opt/openblas/include
For pkg-config to find this software you may need to set:
PKG_CONFIG_PATH: /usr/local/opt/openblas/lib/pkgconfig
$ gem install numo-linalg -- --with-openblas-dir=/usr/local/opt/openblas
require "numo/linalg/use/openblas"
Ubuntu