eigen3@3.3.7: Variants missing/unclear.

[AndyWharton]

Some, possibly related, variant issues:

The eigen3 webpage (​https://ports.macports.org/port/eigen3/summary) and port variants eigen3 does not list the same variants.

Running port variants eigen3 lists duplicate conflicts for some variants:

gcc44: Build using the MacPorts gcc 4.4 compiler
  * conflicts with ... gcc9 gfortran gfortran

It is not documented (at least I could not find it, sorry if I've missed something) what compiler is used for the different components of eigen3. For example +blas +clang90 adds the variants for clang90 and gfortran.

[eborisch (Eric A. Borisch)]

Eigen is by default a header-only install, and no compilers are needed.

If you want to install a compiled BLAS library (+blas) based on Eigen, c++ for compiling the actual library, and fortran (for bindings, if I recall) are needed. But the entire remainder (outside libeigen_blas*) of the Eigen installation remains header-only. I tried to document that with: blas: Build eigen's blas (libeigen_blas*) : needs +gccNN, +g95, or +gfortran

It uses the compilers port group to provide all the different compilers available, so I believe the actual variants available change some based on the OS version.

If you want (+docs) documentation, it uses a compiler again to compile and run code used in the documentation.

Hope that helps.