= Coarse-grid operator
{title2=$A_H=RA_hP$}
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 $R$ transfers residuals to the coarse grid and $P$ 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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