What is the difference between the STATE and OUTPUT of a simulink block. Please explain using one example.

As i was using the enabled subsystem, i want to understand the use of the 'STATES WHEN ENABLING' option. So i want to understand the difference between state and output of a simulink block.

Answer 1

[Iain]

A state is a set of values or conditions. (a column vector)

Output is what is output. The output is some function of the state, and the inputs. That function is often "do nothing".

[vinay kumar]

Hi Ian,

Can you give one example.

[Iain]

The state of a 2nd order system, say, a resonant "LCR" circuit is instantaneous current (or voltage across the resistor) & charge accumulated on the capacitor (or the voltage on the capacitor).

The OUTPUT of that 2nd order system might be: current, charge, the rate of change of current, or any one of three voltages.

[Iain]

A different example is a weight on a spring.

The state is the position and velocity. You input an external force, causing an acceleration, affecting the state (both of them). Viscous forces are generated based on the velocity. Spring forces are generated based on the position.

The output (the bit you are using) might be the acceleration, or it might be the velocity, or the speed, or the force.

[Iain]

The mathematical definition is:

 Updated_State = A * Old_State + B * Input;
 Output = C * Updated_State + D * Input;

So you can get:

 New = [1 0.1; 0.1 1] * [0; 1] + [0; 0.01] * 5;
 Output = [4; 5] * New + [2] * 5;