determining time interval between peaks using a for loop

i have a set of data for volume flow rate (vfr) and plotted a graph vfr against time. i have to find the time interval between peaks using a for loop but am unsure how to write this loop

[jonas]

Do you HAVE to use a loop? Becuse it would be really simple to solve it without a loop. It would also be easier to help you if you upload the data.

[samah khalil]

yeah i have to use a for loop

[jonas]

Nothing I can do if you do not upload the data.

Answer 1

[Adam Danz]

I agree with jonas, a for-loop is unneeded. I also agree that anyone would need a sample dataset to determine the best approach. In the mean time, here's a general approach assuming your data are stored in a vector named vfr.

1) find the peaks using findpeaks() or whatever methed you're already using

[~, loc] = findpeaks(vfr); 

loc will be an index vector that identifies which values in vfr were identified as peaks.

2) Assuming the data in vfr were sampled at a fixed interval 'intv' (say, every 10 ms), all you need to do is determine the number of values between each peak and multiply that number by the sample interval.

timeBetweenPeaks = diff(loc) * intv; 

timeBetweenPeaks is a vector with a length one shorter than loc and is the time between each detected peak.

It's fairly straight forward to turn that into a for-loop but not necessary.

[samah khalil]

how would i go about changing it into a for loop

[Adam Danz]

I'll explain it with words so you can explore some coding which is the best way to learn. But please note that this method is really silly.

loc is a vector of indices such as [10 23 42 99]. That means the 10th , 23rd, etc element of vfr has been identified as a peak. Using a for-loop

for i = __ : __
    [your code]
end

you want to loop through the 2nd element of loc to the end of loc. That is, your loops will be 2 to length(loc). Within each loop, you'll need to get the distance between peak i and peak i-1 and you'll need to store the result in a new vector timeBetweenPeaks. The distance is merely (loc(i)-loc(i-1)) * intv.

For more info on for-loops and examples, see this.