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  2. Morse theory - Wikipedia

    en.wikipedia.org/wiki/Morse_theory

    A less trivial example of a degenerate critical point is the origin of the monkey saddle. The index of a non-degenerate critical point of is the dimension of the largest subspace of the tangent space to at on which the Hessian is negative definite.

  3. Critical point (mathematics) - Wikipedia

    en.wikipedia.org/wiki/Critical_point_(mathematics)

    For a function of n variables, the number of negative eigenvalues of the Hessian matrix at a critical point is called the index of the critical point. A non-degenerate critical point is a local maximum if and only if the index is n, or, equivalently, if the Hessian matrix is negative definite; it is a local minimum if the index is zero, or ...

  4. Catastrophe theory - Wikipedia

    en.wikipedia.org/wiki/Catastrophe_theory

    The degeneracy of these critical points can be unfolded by expanding the potential function as a Taylor series in small perturbations of the parameters. When the degenerate points are not merely accidental, but are structurally stable , the degenerate points exist as organising centres for particular geometric structures of lower degeneracy ...

  5. Sard's theorem - Wikipedia

    en.wikipedia.org/wiki/Sard's_theorem

    In mathematics, Sard's theorem, also known as Sard's lemma or the Morse–Sard theorem, is a result in mathematical analysis that asserts that the set of critical values (that is, the image of the set of critical points) of a smooth function f from one Euclidean space or manifold to another is a null set, i.e., it has Lebesgue measure 0.

  6. Morse–Palais lemma - Wikipedia

    en.wikipedia.org/wiki/Morse–Palais_lemma

    Let (, , ) be a real Hilbert space, and let be an open neighbourhood of the origin in . Let : be a (+)-times continuously differentiable function with ; that is, + (;). Assume that () = and that is a non-degenerate critical point of ; that is, the second derivative () defines an isomorphism of with its continuous dual space by (,).

  7. Cerf theory - Wikipedia

    en.wikipedia.org/wiki/Cerf_theory

    At time =, it has no critical points, but at time =, it is a Morse function with two critical points at =. Cerf showed that a one-parameter family of functions between two Morse functions can be approximated by one that is Morse at all but finitely many degenerate times.

  8. Ginzburg–Landau theory - Wikipedia

    en.wikipedia.org/wiki/Ginzburg–Landau_theory

    In particle physics, any quantum field theory with a unique classical vacuum state and a potential energy with a degenerate critical point is called a Landau–Ginzburg theory. The generalization to N = (2,2) supersymmetric theories in 2 spacetime dimensions was proposed by Cumrun Vafa and Nicholas Warner in November 1988; [ 17 ] in this ...

  9. Hopf bifurcation - Wikipedia

    en.wikipedia.org/wiki/Hopf_bifurcation

    Complex eigenvalues of an arbitrary map (dots). In case of the Hopf bifurcation, two complex conjugate eigenvalues cross the imaginary axis. In the mathematical theory of bifurcations, a Hopf bifurcation is a critical point where, as a parameter changes, a system's stability switches and a periodic solution arises. [1]