For the Armadillo formula is it possible to modify it so that OpenBLAS is used instead of the Accelerate framework on macOS ?
Recent updates to Armadillo allow overriding the use of the Accelerate framework on macOS through options to the cmake based installer.
cmake -D ALLOW_BLAS_LAPACK_MACOS=true .
cmake -D ALLOW_OPENBLAS_MACOS=true .
I don’t know which of the above two options is optimal/applicable to Homebrew (ie. which one would actually detect OpenBLAS or any other BLAS/LAPACK replacement library).
The MacPorts version does the following, which seems to optionally handle OpenBLAS in their specific setup: https://github.com/macports/macports-ports/blob/master/science/armadillo/Portfile