[petsc-users] Spectrum slicing, Cholesky factorization for positive semidefinite matrices

[Jan Grießer]

Hello, everybody,
i want to use the spectrum slicing method in Slepc4py to compute a subset
of the eigenvalues and associated eigenvectors of my matrix. To do this I
need a factorization that provids the Matrix Inertia. The Cholesky
decomposition is given as an example in the user manual. The problem ist
that my matrix is not positive definit but positive semidefinit (Three
eigenvalues are zero). The PETSc user forum only states that for the
Cholesky factorization a symmetric matrix is zero, but as far is i remember
the Chosleky factorization is only numerical stable for positive definite
matrices. Can i use an LU factorization for the spectrum slicing, although
the PETSc user manual states that the Inertia is accessible when using
Cholseky? Or can is still use Chollesky?
Greetings Jan
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