## Preconditioners - PC: Examples

The Scalable Linear Equations Solvers (KSP) component provides an easy-to-use interface to the combination of a Krylov subspace iterative method and a preconditioner (in the KSP and PC components, respectively) or a sequential direct solver. KSP users can set various preconditioning options at runtime via the options database (e.g., -pc_type jacobi ). KSP users can also set PC options directly in application codes by first extracting the PC context from the KSP context via KSPGetPC() and then directly calling the PC routines listed below (e.g., PCSetType() ). PC components can be used directly to create and destroy solvers; this is not needed for users but is for library developers.

nn.h
nn.c
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