follow dev43, 1. refer to the framework of GMG (geometric multimesh) and the construction methods of P matrix and R matrix of the simplest AMG (algebraic multimesh), and give an example (refer to ./test/ test-dev44-gmg.ipynb); 2. after reading the discussion of the eigen spectra of multiple operators (matvec) in <Multigrid for Chiral Lattice Fermions-Domain Wall>, in order to repeat the relevant work, a multi-lattice-sizes (the minimum was temporarily set as 4,4,4,4) & multi-precision BISTABCG solver was realized as a paving work (see./test/ test-dev44-demo.ipynb). :)