Fast eigenvalue calculations in a massively parallel plasma turbulence code

Additionally, eigenvalue computations can provide new insight into the properties of plasma turbulence. The latter is driven by a number of different unstable modes, including dominant and subdominant ones, that can be determined employing SLEPc. This computation is more challenging from the numerical point of view, since these eigenvalues can be considered interior, and also because the linearized operator is available only in implicit form. We analyze the feasibility of different strategies for computing these modes, including matrix-free spectral transformation as well as harmonic projection methods.