Remove geometric multigrid Laplacian inversion solver

CHANGELOG.md

@@ -15,6 +15,7 @@
   ```console
   $ bout-upgrader v6 v6_upgrader file/to/update.cxx
   ````
+- Removed `multigrid` Laplacian inversion solver
 
 ## [v5.2.0](https://github.com/boutproject/BOUT-dev/tree/v5.2.0
 

CMakeLists.txt

@@ -248,10 +248,6 @@ set(BOUT_SOURCES
     ./src/invert/laplace/impls/hypre3d/hypre3d_laplace.hxx
     ./src/invert/laplace/impls/iterative_parallel_tri/iterative_parallel_tri.cxx
     ./src/invert/laplace/impls/iterative_parallel_tri/iterative_parallel_tri.hxx
-    ./src/invert/laplace/impls/multigrid/multigrid_alg.cxx
-    ./src/invert/laplace/impls/multigrid/multigrid_laplace.cxx
-    ./src/invert/laplace/impls/multigrid/multigrid_laplace.hxx
-    ./src/invert/laplace/impls/multigrid/multigrid_solver.cxx
     ./src/invert/laplace/impls/naulin/naulin_laplace.cxx
     ./src/invert/laplace/impls/naulin/naulin_laplace.hxx
     ./src/invert/laplace/impls/pcr/pcr.cxx

include/bout/invert_laplace.hxx

@@ -66,7 +66,6 @@ constexpr auto LAPLACE_PETSCAMG = "petscamg";
 constexpr auto LAPLACE_PETSC3DAMG = "petsc3damg";
 constexpr auto LAPLACE_HYPRE3D = "hypre3d";
 constexpr auto LAPLACE_CYCLIC = "cyclic";
-constexpr auto LAPLACE_MULTIGRID = "multigrid";
 constexpr auto LAPLACE_NAULIN = "naulin";
 constexpr auto LAPLACE_IPT = "ipt";
 constexpr auto LAPLACE_PCR = "pcr";

manual/sphinx/user_docs/laplacian.rst

@@ -41,8 +41,6 @@ implementations are listed in table :numref:`tab-laplacetypes`.
    | petsc3damg             | Serial/parallel. Solves full 3D operator (with               | PETSc (section :ref:`sec-PETSc-install`) |
    |                        | y-derivatives) with algebraic multigrid.                     |                                          |
    +------------------------+--------------------------------------------------------------+------------------------------------------+
-   | multigrid              | Serial/parallel. Geometric multigrid, no Boussinesq          |                                          |
-   +------------------------+--------------------------------------------------------------+------------------------------------------+
    | `naulin                | Serial/parallel. Iterative treatment of non-Boussinesq terms |                                          |
    | <sec-naulin_>`__       |                                                              |                                          |
    +------------------------+--------------------------------------------------------------+------------------------------------------+
@@ -87,11 +85,10 @@ and :math:`n_z` are the number of grid-points in the :math:`x` and
 :math:`z` directions respectively.
 
 
-In the second approach, the full :math:`2`\ -D system is solved. The
-available solvers for this approach are 'multigrid' using a multigrid
-algorithm; 'naulin' using an iterative scheme to correct the FFT-based
-approach; or 'petsc' using KSP linear solvers from the PETSc library
-(this requires PETSc to be built with BOUT++).
+In the second approach, the full :math:`2`\ -D system is solved. The available
+solvers for this approach are ``naulin`` using an iterative scheme to correct
+the FFT-based approach; or ``petsc`` using KSP linear solvers from the PETSc
+library (this requires PETSc to be built with BOUT++).
 
 
 The `Laplacian` class is defined in ``invert_laplace.hxx`` and solves
@@ -780,14 +777,6 @@ Cyclic algorithm
 This is now the default solver in both serial and parallel. It is an FFT-based
 solver using a cyclic reduction algorithm.
 
-.. _sec-multigrid:
-
-Multigrid solver
-~~~~~~~~~~~~~~~~
-
-A solver using a geometric multigrid algorithm was introduced by projects in
-2015 and 2016 of CCFE and the EUROfusion HLST.
-
 .. _sec-naulin:
 
 Naulin solver