State-transition matrix
Encyclopedia
In control theory
Control theory
Control theory is an interdisciplinary branch of engineering and mathematics that deals with the behavior of dynamical systems. The desired output of a system is called the reference...

, the state-transition matrix is a matrix whose product with the state vector at an initial time gives at a later time . The state-transition matrix can be used to obtain the general solution of linear dynamical systems. It is also known as the matrix exponential
Matrix exponential
In mathematics, the matrix exponential is a matrix function on square matrices analogous to the ordinary exponential function. Abstractly, the matrix exponential gives the connection between a matrix Lie algebra and the corresponding Lie group....

.

Overview

Consider the general linear state space
State space (controls)
In control engineering, a state space representation is a mathematical model of a physical system as a set of input, output and state variables related by first-order differential equations...

 model

The general solution is given by

The state-transition matrix , given by

where is the fundamental solution matrix that satisfies

is a matrix that is a linear mapping onto itself, i.e., with , given the state at any time , the state at any other time is given by the mapping

While the state transition matrix φ is not completely unknown, it must always satisfy the following relationships:
and
for all and where is the identity matrix
Identity matrix
In linear algebra, the identity matrix or unit matrix of size n is the n×n square matrix with ones on the main diagonal and zeros elsewhere. It is denoted by In, or simply by I if the size is immaterial or can be trivially determined by the context...

.

And φ also must have the following properties:
1.
2.
3.
4.


If the system is time-invariant, we can define φ as:


In the time-variant case, there are many different functions that may satisfy these requirements, and the solution is dependent on the structure of the system. The state-transition matrix must be determined before analysis on the time-varying solution can continue.
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