Lapack, scalapack, blas, gcc, g++, and gfortran are all available.
PureOS deviated very little from Debian, so if you can find it in Debian (and it’s free/open source), then chances are you can find it in PureOS.
Just note that PureOS does NOT support 32-bit architecture.
Though aside from some smaller analysis, I wouldn’t expect you to be doing a whole lot on your laptop anyway. Most of that sort of things tends to happen on clusters, no? That’s how it is for my branch of particle physics anyway.