pan 
class="cmbx-12">Remark 1. </span><span 
class="cmr-12">Coarsest-level solvers based on the LU factorization, such as those</span>
<span 
class="cmr-12">implemented in UMFPACK, MUMPS, SuperLU, and SuperLU</span><span 
class="cmr-12">_Dist, usually lead to</span>
<span 
class="cmr-12">smaller numbers of preconditioned Krylov iterations than inexact solvers, when the</span>
<span 
class="cmr-12">linear system comes from a standard discretization of basic scalar elliptic PDE</span>
<span 
class="cmr-12">pr