The LAPACK compatibility library is enabled with EIGEN_BUILD_LAPACK and requires EIGEN_BUILD_BLAS. Its optional numerical tests (EIGEN_ENABLE_LAPACK_TESTS) require a Fortran compiler and the LAPACK test data.

The tests and their summary run through CMake/CTest without Python. LAPACK_Test_Summary waits for the registered numerical tests and combines only their expected output files into TESTING/testing_results.txt in the LAPACK build directory. It fails when the output reports numerical errors, illegal-argument or INFO diagnostics, when an expected output is missing, or when no numerical tests were analyzed. Selecting LAPACK_Test_Summary alone also runs its numerical tests through a CTest fixture. If a numerical driver fails to execute successfully, CTest skips the summary.

Balancing tests contribute their example counts and fail on nonzero INFO/ILO error counts or non-finite maximum errors. Their finite maximum errors remain in the combined report; these drivers do not specify a pass/fail threshold.

The numerical tests use unmodified LAPACK 3.12.1 sources, downloaded with a pinned SHA-256 hash. They exercise Eigen's BLAS/LAPACK implementations, using reference LAPACK for the remaining routines. All test cases remain enabled; known numerical and test-driver failures are reported by the summary.