find onest and end of wave ?

hello

how i can find the onest (the beginning) and the end of wave if i have the peaks only?

[KSSV]

Show us how your data is. Pictorial example with your expectations will help us to help you.

[yasmeen hadadd]

Thnk you for replying :)

if i have an ecg signal and i find the peaks of every wave and i will find the onest and end of each wave , please see the figure bellow

Answer 1

[Bjorn Gustavsson]

You cannot in a strict sense. You will have to settle for the first and last wave-crest, or set some arbitrary threshold for the wave-amplitude (10% of the peak, of the peak-to-peak, whatever). That this is impossible follows from the fact that functions like f(x-vt) solves the wave-equation - we can for example set f to be some sequence of Gaussian pulses moving to the right, and since a Gaussian has infinite support where it starts or ends becomes a question of where you set your threshold.

In practice if you have some natural noise-level in your measurements this might give you some sensible reason to select a threshold.

HTH

[yasmeen hadadd]

yes i look to find the relationship btween peaks , the beginning and the end of wave by Gaussian distribution.

[Bjorn Gustavsson]

Ok, take it step by step.

1, Identify the peak

2, find s - the full-widths at 1/e,

3, take the data out to +/- 2s or 3s.

4, fit a Gaussian to that data, using fminsearch.

This should give you the Gaussian that is best fitting to the peak. Then you just have to select a threshold where you consider the "wave to start".

HTH

[yasmeen hadadd]

yes yes yes

thank you very very much

[Bjorn Gustavsson]

You're ever so welcome.