copied the templates

mgrid_2/README.md

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+# gmgrid: Geometric multigrid on CPU (OpenMP)
+
+### Status on 2025-May-14
+ - The multigrid part is deactivated via `*#undef MG` in *main.cpp* and so only a simple Jacobi iteration is performed as solver.
+ - `make run`
+ - or `main.GCC_ levels`  with number of `levels` in [0,7].
+
+### Data structures/implementation for GPU
+ - use data structures from cg_2:Framework for preconditioned solvers on GPU and CPU
+ - suggested: class vec from vdop_gpu.h
+ - suggested: class CRS_Matrix_GPU from crsmatrix_gpu.h
+ - use cuBLAS, cuSPARSE and more libraries whenever possible.
+ 
+### current code structure
+ - *main.cpp*
+ - *binaryIO.cpp*    : reads CRS matrix and vector from files
+ - *vdop.cpp*        : some basic vector operations on CPU, also in *utils.h*
+ - *geom.cpp*        : reads the coarse geometry, performes mesh handling and includes mesh hierarchy
+ - *getmatrix.cpp*   : compressed row storage matrix and its generation from a 2D mesh
+ - *cuthill_mckee_ordering.cpp* : graph reordering to minimize the bandwidth
+ - *jacsolve.cpp*    : Jacobi solver/smoother for a linear system of equations with CRS matrix; multigrid solver
+ - *elements.cpp*    : more general elements - experimental. Try with *el_main.cpp*
+ - *generateCRS.cpp* : Reads mesh files and generates files output with stiffness matrix (Laplace) and right hand side.
+