It is a similar notion, but it refers to two fixed points, and . The condition satisfied by
is replaced with:
This notion is not symmetric with respect to and .
Homoclinic and heteroclinic intersections
When the invariant manifolds and , possibly with , intersect but there is no homoclinic/heteroclinic connection, a different structure is formed by the two manifolds, sometimes referred to as the homoclinic/heteroclinic tangle. The figure has a conceptual drawing illustrating their complicated structure. The theoretical result supporting the drawing is the
lambda-lemma. Homoclinic tangles are always accompanied by a
Smale horseshoe.
Definition for continuous flows
For continuous
flows, the definition is essentially the same.
Comments
There is some variation in the definition across various publications;
Historically, the first case considered was that of a continuous flow on the
plane, induced by an
ordinary differential equation. In this case, a homoclinic connection is a single
trajectory that converges to the fixed point both forwards and backwards in time. A
pendulum in the absence of
friction is an example of a mechanical system that does have a homoclinic connection. When the pendulum is released from the top position (the point of highest potential energy), with infinitesimally small velocity, the pendulum will return to the same position. Upon return, it will have exactly the same velocity. The time it will take to return will increase to as the initial velocity goes to zero. One of the demonstrations in the
pendulum article exhibits this behavior.
Significance
When a dynamical system is perturbed, a homoclinic connection splits. It becomes a
disconnected invariant set. Near it, there will be a chaotic set called
Smale's horseshoe. Thus, the existence of a homoclinic connection can potentially lead to
chaos. For example, when a pendulum is placed in a box, and the box is subjected to small horizontal oscillations, the pendulum may exhibit chaotic behavior.