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A state variable is one of the set of variables that are used to describe the mathematical "state" of a dynamical system. Intuitively, the state of a system describes enough about the system to determine its future behaviour. Models that consist of coupled firstorder differential equations are said to be in statevariable form.^{[1]}
Examples[edit]
 In mechanical systems, the position coordinates and velocities of mechanical parts are typical state variables; knowing these, it is possible to determine the future state of the objects in the system.
 In thermodynamics, a state variable is also called a state function. Examples include temperature, pressure, volume, internal energy, enthalpy, and entropy. In contrast heat and work are not state functions, but process functions.
 In electronic circuits, the voltages of the nodes and the currents through components in the circuit are usually the state variables.
 In ecosystem models, population sizes (or concentrations) of plants, animals and resources (nutrients, organic material) are typical state variables.
Control systems engineering[edit]
In control engineering and other areas of science and engineering, state variables are used to represent the states of a general system. The state variables can be used to describe the state space of the system. The equations relating the current state and output of a system to its current input and past states are called the state equations. The state equations for a linear time invariant system can be expressed using coefficient matrices:
 R^{N*N}, R^{N*L}, R^{M*N}, R^{M*L},
where N, L and M are the dimensions of the vectors describing the state, input and output, respectively.
Discretetime systems[edit]
The state variable representing the current state of a discretetime system (i.e. digital system) is , where n is the discrete point at which the system is being evaluated. The discretetime state equations are
 , which describes the next state of the system (x[n+1]) with respect to current state and inputs u[n] of the system.
 , which describes the output y[n] with respect to current states and inputs u[n] to the system.
Continuous time systems[edit]
The state variable representing the current state of a continuoustime system (i.e. analog system) is , and the continuous time state equations are
 , which describes the next state of the system with respect to current state x(t) and inputs u(t) of the system.
 , which describes the output y(t) with respect to current states x(t) and inputs u(t) to the system.
See also[edit]
References[edit]
 ^ William J. Palm III (2010). System Dynamics (2nd ed.). p. 225.
Lecture  45 StateVariable Methods (1) Lecture Series on Networks and Systems by Prof.V.G.K.Murti, Department of Electrical Engineering, IIT Madras. For More details on NPTEL visit http://nptel.ii...  State Space Representation ( Dynamic Systems )  Mechanical Engineering State Space Representation Dynamic Systems.  Lecture 48 State Variable Methods (4) Lecture Series on Networks and Systems by Prof.V.G.K.Murti, Department of Electrical Engineering, IIT Madras. For More details on NPTEL visit http://nptel.ii...  Synthesizers.com Q107 State Variable Filter Here is a brief demonstration of the capabilities and sound of the Synthesizers.com state variable filter.  Introduction to State Space (State Variable) Representation Develops, by example, the state variable representation of a 3rd order LTI system, beginning with it's scalar differential equation, creating a signal block ...  Proof: S (or Entropy) is a valid state variable Prroof that S (or entropy) is a valid state variable. More free lessons at: http://www.khanacademy.org/video?v=sPz5RrFus1Q.  Lecture  46 StateVariable Methods(2) Lecture Series on Networks and Systems by Prof.V.G.K.Murti, Department of Electrical Engineering, IIT Madras. For More details on NPTEL visit http://nptel.ii...  Manhattan Analog  State Variable VCF Here's my overview video for the SVVCF (Stave Variable Voltage Controlled Filter) from Manhattan Analog. Check out the sound and patches in the video, feel f...  Intellijel  uVCF State Variable FIlter demo General overview of the uVCF filter including the LowPass, Bandpass and Highpass outputs, sine VCO functionality and FM.  Lec47 StateVariable Equations Lecture Series on Control Engineering by Prof. S.D. Agashe, Department of Electrical Engineering,IIT Bombay. For more details on NPTEL visit http://nptel.iit... 

Business Wire (press release)
Wed, 15 Oct 2014 03:41:15 0700
State estimation is the process of assigning a value to an unknown system state variable, based on measurements from that system based on preset criteria. The process involves imperfect measurements that are redundant and the process of estimating the ...
 
GameDev.net
Tue, 30 Sep 2014 12:30:17 0700
Dozens of questions need to be asked  is the problem an OpenGL state variable issue, a shader issue, a problem with your loaded models/textures, etc? Being able to quickly answer these questions would save me truckloads of time. I also think using a ...
 
Lincoln Journal Star
Sun, 28 Sep 2014 03:10:28 0700
Nebraska was the 37th state admitted to the union, so the Journal Star staff compiled a list of 37 icons that represent our state's people, history and heritage. We decided 37 was kind of an odd number, so we asked readers to add 13 more. Here is our ...
 
GameDev.net
Sun, 05 Oct 2014 01:24:47 0700
i think you're tracking two states (moving and attacking) with one state variable. as frob says, you can enumerate the combos as a single state variable, or use individual state variables, as described by sean: If you have completely independent ...
 
GameDev.net
Tue, 07 Oct 2014 08:23:55 0700
I don't know much about Swift, but you can have a state variable (that can be START, PLAY, GAME_OVER) and in your update method you can check what the state is and respond differently. Like so: (void)update { if (self.state == START) { if (button ...

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