how to calculate variance of a signal after it reaches a steady state value...

The signal for which the variance is to be calculated is in the base workspace in timeseries format. i want to calculate the variance only after 0.5 seconds. How to do it?

[Cedric]

The variance of a time series at steady-state? Well, what is your definition of steady-state?

[Vidhya Dharshini]

yeah.......i can get you.......you mean steady state refers to the property of not changing with time........for my case i am designing a speed controller for a motor......when i set a reference speed of 20000, the speed starts increasing from 0 to 20000. it oscillates around 20000. and i want to calculate the variance only after it reaches my reference value........ i should have mentioned it as desired value instead of steady state value in the question........thank u.......i have calculated the variance.....

[Image Analyst]

firstIndex = find(speed >= 20000, 1, 'first');
theVariance = var(speed(firstIndex : end));

Answer 1

[Image Analyst]

What element does 0.5 seconds occur at? Let's say it's element 42, so then you do

varSteadyState = var(yourSignal(42:end));

Let's say you have a vector t with the times, and a vector yourSignal with the signal value. You can find the index for which t equals or passes 0.5 seconds like this:

startingElement = find(t>=0.5, 1, 'first');
varSteadyState = var(yourSignal(startingElement :end));

[Vidhya Dharshini]

Thank u so much sir.........

[Jessica]

Hi just one question how did you calculate the steady state ?

Thank You