how to find duration of peak; starting and ending points

I've used findpeaks to isolate the largest peak in my signal. I wanted some help in finding the duration of the peak aka the starting and ending points of this peak, so that I could calculate area under curve? Right now Im having to visually inspect and pick arbitrary points to define this start and end points.

Answer 1

[Star Strider]

Experiment with ths ischange function, and if you have the Signal Processing Toolbox, the findchangepts function.

[Raheema Al Karim Damani]

Thank you for your response. I used findchangepts but since I have so much noise in my signal, I could not get the correct index. I've isolated this peak using the findpeak function:

[pks,loc,wid,p] = findpeaks(inv, 'SortStr','descend','NPeaks',1)

Can you advise on how I can apply findchangepts to only this peak. 

[Raheema Al Karim Damani]

here is the limits when I use 2 maxnumchanges

[Star Strider]

You will need to experiment with the functions. They cannot guess what you are thinking, and so they need to have some guidance.

[Raheema Al Karim Damani]

I appreciate your advice, but is there anyway to automate this process, instead of relying on findchangepts to create index for the peak because I have about 50 more plots.

[Star Strider]

In the plot you posted, there are several things findchangepts can consider to be change points.

The findchangepts function has a number of name-value pair arguments that you can use to tell it what you want it to do. The 'Statistic' and 'MinDistance' arguments are the ones I usually use. A different subset may be more appropriate for your purposes.

[Raheema Al Karim Damani]

Thank you your advice was helpful. The statistics arguments is really helpful in the findchangepts functions.

[Star Strider]

As always, my pleasure!

Answer 2

[Sindar]

widths are an optional output from findpeaks:

[pks,locs,widths,~] = findpeaks(data);

[Sindar]

Alternatively, you could potentially define the starting and ending points using findpeaks on the negative of your data.

[Raheema Al Karim Damani]

I believe that it finds the widths from the half prominence or half height, which would not accurately characterize the starting and ending points.

Also, I would like to find the index (x values) of the peak based on start and end points

Answer 3

[Alexis]

I had a similar issue, although I was working with biological signals. You could try the function I wrote to solve my problem: https://uk.mathworks.com/matlabcentral/fileexchange/81066-breathtimes?s_tid=srchtitle

Answer 4

[Lam Ha]

Hi, I'm doing my research and meet the same problems as you. Have you calculated the peak duration? Can you share to me how to calculate the peak duration? Thank you so much in advance