In control theory, a system is said to possess one
In control theory, a system is said to possess one of these if any eigenvalues of the state matrix have real parts greater than zero. A two- stream one may develop when a particle beam has a velocity distribution that peaks far away from the peak of the distribution of the medium through which the beam is passing.  The sausage type arises during attempts to pinch a plasma, and the Rayleigh Taylor type is the exponential growth of waves in a heavy fluid supported by a light one. All these phenomena are types of, FTP, what general behavior, characterized by boundless growth of perturbations within a system?
In control theory, a system is said to possess one of these if any eigenvalues of the state matrix have real parts greater than zero.
instability