[petsc-users] Calculating inertias

[Jose E. Roman]

You can do this directly in PETSc. Create a KSP object with PREONLY and PCCHOLESKY (or just a PC object). Then call KSPSetUp (or PCSetUp) and extract the factored matrix with PCFactorGetMatrix(). Then call MatGetInertia() on the factored matrix. Repeat this for each value of E.

I guess it can be even shorter if you call MatCholeskyFactor() directly.

Jose


> El 24 mar 2020, a las 11:07, Perceval Desforges <perceval.desforges at polytechnique.edu> escribió:
> 
> Dear petsc developers,
> 
> I am interested in calculating the inertias of matrixes. Specifically, for a certain matrix A, and for different real numbers E, I want to calculate the inertias of (A - E * I), in order to get the number of eigenvalues less than E. 
> 
> In order to do this I have been setting up a slepc EPS object with spectrum slicing, and using EPSKrylovSchurGetInertias. I realize this is a bit convoluted, and was wondering if there is a better way to do this?
> 
> Best regards,
> 
> Perceval,
> 
> P.S. my last email seems to not have been sent (I couldn't find it in the archives) so I am trying again...
>