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Our method is a kind of exact interpolation scheme by Achi Brandt et al. In the exact interpolation scheme, for x being the fine‐level approximation of the solution, the coarse‐space V = V(x) is constructed so that x satisfies x∈V. We achieve it simply by adding the vector x as a first column of the prolongator. (The columns of the prolongator P form a computationally relevant basis of the coarse‐space...