"Kong, Fande" <fande.k...@inl.gov> writes: > Hi Developers, > > Any reason to force users provide a matrix which does not miss any diagonal > entries when using a LU-type solver?

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Automatically adding the entries for incomplete factorization is a slight increase in complexity and means that "ILU(0)" actually has some fill. Note that a literal ILU(0) cannot work if there are missing diagonal entries. It's probably not a significant code complexity difference for LU. > Sometime, it is impossible to have all diagonal entries in a matrix, that > is, the matrix has to miss some diagonal entries. For example, there is a > saddle-point matrix from the discretization of incomprehensible equations, > and the lower part of the matrix is a zero block. The matrix usually looks > like: > > | A B^T | > | B 0 | Just insert explicit zeros on the diagonal.

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