Variable dynamic mode decomposition for estimating time eigenvalues in nuclear systems

An extension to the Dynamic Mode Decomposition (DMD) method for calculating time eigenvalues (also known as alpha eigenvalues) that removes the requirement of a constant time step is derived and demonstrated. The new method, called variable-dynamic mode decomposition (V-DMD), is shown to be accurate when computing eigenvalues for systems that were infeasible with DMD due to a large separation in time scales. The alpha eigenvalues of an infinite medium neutron transport problem with delayed neutrons and consequently having multiple, very different relevant time scales are computed. Furthermore, V-DMD is shown to be of similar accuracy to the original DMD approach when computing eigenvalues in other systems where DMD can be used. (authors)