calculating the time constant

I have a vector represent a step change, and I want to calculate the time constant of it, "the time it takes to reach 63%". the vector that represent the step change is as below:

y = 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0.0000 0.0001 0.0006 0.0029 0.0108 0.0266 0.0583 0.1212 0.2361 0.3877 0.5089 0.6059 0.6833 0.7453 0.7948 0.8343 0.8660 0.8913 0.9115 0.9276 0.9405 0.9509 0.9591 0.9657 0.9710 0.9752 0.9786 0.9813 0.9834 0.9851 0.9865 0.9876 0.9885 0.9892 0.9898 0.9902 0.9906 0.9909 0.9911 0.9913 0.9914 0.9915 0.9916 0.9917 0.9918 0.9918 0.9918 0.9919 0.9919 0.9919 0.9919 0.9920 0.9920

if you made a plot to the Y vector in the matlab it will give you step function from 0 to 0.9405, I just want to calculate the time it takes to reach 0.63 from the step, which by eye can be detrmind at aprox. 27

I need a formula to calculate it automatically please advise

[Walter Roberson]

Please examine the guide to tags and retag this question; see http://www.mathworks.co.uk/matlabcentral/answers/43073-a-guide-to-tags

[Azzi Abdelmalek]

You mean 63% from the y(end)

Answer 1

[Azzi Abdelmalek]

 yi=y(end)
 idx=max(find(abs(y-yi)>=0.37*yi))

% idx the corresponding index

[Hassan]

Thanks alot Azzi, It really worked very well... Appreciating all your efforts.

Answer 2

[Ákos]

Hi!

I have an input and an output vector, for example:

in=[0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 1; 1; 1; 1; 1; 1; 1; 1; 1; 1; 1; 1; 1; 1; 1; 1; 1; 1; 1; 1]

out=[0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 2; 12; 17; 20; 21; 22; 22; 22; 22; 22; 22; 22; 22; 22; 22; 22; 22]

If you want to see it in a figure, type the following code to the Command Window:

in=[0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 1; 1; 1; 1; 1; 1; 1; 1; 1; 1; 1; 1; 1; 1; 1; 1; 1; 1; 1; 1];
out=[0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 2; 12; 17; 20; 21; 22; 22; 22; 22; 22; 22; 22; 22; 22; 22; 22; 22];
x=(1:1:30);
plot(x,in,'red')
hold
plot(x,out,'blue')
hold

I would like to determinate the delay and the time constant. I have System Identification Toolbox, and I can determinate the delay in GUI mode (Td=2.864), but I would like to determinate it in a matlab script. Which functions have to use, and how? Maybe I have to use the delayest function, but it doesn't works in this way:

DATA=iddata(out,in,0.1)
delayest(DATA)

The result is 0.

So I think this is not the right way. Can somebody write me an example to this two vector?

Thanks in advance!

[Azzi Abdelmalek]

Ákos, This is expected to be an answer. If you want to get more chance to have an answer, post a new question.