 Novikov–Shubin invariant

The Novikov–Shubin invariants are a set of topological invariants associated with certain types of elliptic operators, particularly in the context of non-compact manifolds or manifolds with boundaries. They arise in the study of the heat equation and index theory, particularly in connection with the theory of elliptic partial differential operators and noncommutative geometry. These invariants can be thought of as a generalization of classical numerical invariants associated with the index of elliptic operators.