In mathematics, **stability theory** addresses the stability of solutions of differential equations and of trajectories of dynamical systems under small perturbations of initial conditions. The heat equation, for example, is a stable partial differential equation because small perturbations of initial data lead to small variations in temperature at a later time as a result of the maximum principle. More generally, a theorem is stable if small changes in the hypothesis lead to small variations in the conclusion. One must specify the metric used to measure the perturbations when claiming a theorem is stable. In partial differential equations one may measure the distances between functions using Lp norms or the sup norm, while in differential geometry one may measure the distance between spaces using the Gromov-Hausdorff distance.

In dynamical systems, an orbit is called **Lyapunov stable** if the forward orbit of any point is in a small enough neighborhood or it stays in a small (but perhaps, larger) neighborhood. Various criteria have been developed to prove stability or instability of an orbit. Under favorable circumstances, the question may be reduced to a well-studied problem involving eigenvalues of matrices. A more general method involves Lyapunov functions.

Read more about Stability Theory: Overview in Dynamical Systems, Stability of Fixed Points, Lyapunov Function For General Dynamical Systems, See Also

### Famous quotes containing the words stability and/or theory:

“Traditions are the “always” in life—the rituals and customs that build common memories for children, offer comfort and *stability* in good times and bad, and create a sense of family identity.”

—Marian Edelman Borden (20th century)

“[Anarchism] is the philosophy of the sovereignty of the individual. It is the *theory* of social harmony. It is the great, surging, living truth that is reconstructing the world, and that will usher in the Dawn.”

—Emma Goldman (1869–1940)