A coarse-grid operator represents the equation solved for an error correction on the coarser level of a multigrid method. It may be obtained by rediscretizing the differential equation at the coarse spacing, or through the Galerkin coarse-grid operator formula displayed above. Here transfers residuals to the coarse grid and transfers coarse corrections to the fine grid. The right-side and operator scalings must be consistent with the chosen transfer convention.
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