Remove LAPACK dependency

[Connor-Bowley]

It am unable to find where lapack is being used in this extension, and having LAPACK as a dependency is a bit of overhead with needing fortran and all.

[styner]

I don't think GROUPS is needing LAPACK (not 100% sure), this might be historically in there as the SPHARM-PDM extension needs LAPACK (and GROUPS usually follows SPHARM-PDM)

[sjh26]

SPHARM-PDM specifies its own LAPACK dependency, so it shouldn't be needed here as well.

[jcfr]

The GroupwiseRegistration explicitly requires the lapack function ssyev_ in the implementation of GroupwiseRegistration::eigenvalues:

https://github.com/NIRALUser/GROUPS/blob/1263afc128b4ebf4442695af569d1832432e3d18/Modules/CLI/Groups/GroupwiseRegistration.cpp#L1168-L1178

Related links:

• https://netlib.org/lapack/explore-html/d3/d88/group__real_s_yeigen_ga63d8d12aef8f2711d711d9e6bd833e46.html
• https://github.com/Reference-LAPACK/lapack/blob/77a0ceb6c9a3c757e7039027f1f324e2811e6ee0/SRC/ssyev.f

[jcfr]

Use of GroupwiseRegistration::eigenvalues is the following:

GROUPS::main
  -> GroupwiseRegistration::run
    -> GroupwiseRegistration::optimization
      -> cost_function::operator()
        -> GroupwiseRegistration::cost
          -> GroupwiseRegistration::entropy
            -> GroupwiseRegistration::eigenvalues
              -> ssyev_

[jcfr]

Closing. This was addressed by @allemangD replacing LAPACK ssyev with Eigen EigenSolver