Changelog

Release includes PRs 12, 14, 15, 16, 19, 21, 22, 23, 24, 25, 26

Interface breaking changes

• Centralized settings objects — PR 21: Centralized Settings Types for Solver and Stability Check
  solver and stability_check now accept a single settings object (solver_settings_type / stability_settings_type) instead of long optional argument lists. Initialize via provided init helpers and pass the object across language boundaries.

• Callback signatures & integer error codes — PR 12: Modified callback functions to enable return of error code
  Callbacks now return integer status codes (0 = success) and must write outputs into caller-provided buffers (pointer-in/out, C-style). Python and C interfaces were updated to match.

• Memory ownership & optional kappa — PR 14: Improved memory handling
  Variable-size arrays are heap-allocated; the library prefers caller-provided buffers (zero-copy), otherwise it allocates temporaries and frees them. stability_check only writes kappa if caller supplies memory (pass NULL/omit if not needed).

• Solver/diag keyword change & reproducibility — PR 23: Add subsystem and diagonalization solver keywords and random seed argument for stability check
  Boolean solver-selection flags were replaced by explicit string keywords (subsystem_solver, diag_solver) and seed was added to control random trial vectors for stability check.

Migration checklist

1. Adopt settings objects (PR 21)

   • Fortran: create and init() solver_settings_type / stability_settings_type and pass them to the routines.
   • C: use solver_settings_init() / stability_settings_init() helpers.
   • Python: use SolverSettings() / StabilitySettings().

2. Update callbacks (PRs 12, 14, 26)

   • update_orbs must write grad and h_diag in-place and return an integer status.
   • hess_x must write into hx and return an integer status.
   • precond must write into precond_residual and return an integer status.
   • obj_func returns an integer status.

3. Handle kappa explicitly (PR 14)

   • If you need the descent direction, allocate and pass kappa. If not, omit or pass NULL/None.

4. Replace solver booleans with strings (PR 23)

   • Use subsystem_solver = one of: "davidson", "jacobi-davidson", "tcg".
   • Use diag_solver = one of: "davidson", "jacobi-davidson".

5. Rebuild C/C++ callers and update packaging (PRs 24, 26)

   • Rebuild against the new header; adjust code where void* fields were replaced by typed function-pointer fields.
   • If supplying custom BLAS/LAPACK, set INTEGER_SIZE in CMake; update downstream packaging for the new library-name suffixes.
     
Error codes follow the library's structured scheme (origin + error number). For precise usage examples in Fortran, C, and Python, please refer to the updated README.md included in this release.

Other changes

• PR 15 — Change CMake project name and change handling of binary files for system tests.
• PR 16 — CMake: Add BUILD_SHARED_LIBS and BUILD_TESTS options.
• PR 19 — Alphabetize unit tests (corresponds to test ordering).
• PR 22 — Add reference to README.
• PR 24 — Improved CMake library names, versioning and BLAS/LAPACK handling (INTEGER_SIZE, LIB_SUFFIX, VERSION/SOVERSION).
• PR 25 — Support for Installed, Editable, and Development (CMake) Python Usage.
• PR 26 — The public C header was refactored for stronger typing (function-pointer fields replace some void*) and the CMake build system was refactored.