On 07.17.2014 16:41, Jed Brown wrote: > Jozsef Bakosi <[email protected]> writes: > > > Hi folks, > > > > I have a matrix as a result of a finite element discretization of the > > Poisson > > operator and associated right hand side. As it turns out, the matrix is > > symmetric but not positive definite since it has at least two negative small > > eigenvalues. I have been solving this system without problem using the > > conjugate > > gradients (CG) algorithm with ML as a preconditioner, but I'm wondering why > > it > > works. > > Is the preconditioned matrix > > P^{-1/2} A P^{-T/2} > > positive definite?
How would you extract P?
