How to select values in an array until a known value

Hello,

I will explain my problem. I have a 1x1701 sampled array "resampled_WF", once I found the max value of this array ("peak_WF"), I set a threshold 0.7*peak_WF, and I would like to select the farthest value in the array that gets nearer to this threshold.

Example:

As you can see, I was able to select ony the first value that resembles... but I would like to get the last one (around t=2 sec).

I tried to flip the array with "flip" function:

WF_threshold_input = 0.7*peak_WF;
flip_resampled_WF = flip(resampled_WF);
diff_peak_threshold = peak_WF - WF_threshold_input; %power loss at 70% power reduction
diff_peak_WF = peak_WF - flip_resampled_WF;
min_diff_threshold = min(abs(diff_peak_WF-diff_peak_threshold));

Doing that, MATLAB computes minimum difference on the whole array, I would like to stop at the first value, not considering further values.

I tried to select values with values<= WF_threshold_input, but again it selects over the whole dataset.

How can I select the value properly?

Thanks!!

Answer 1

[Cris LaPierre]

I would probably use find.

1. Identify the index of the peak value
2. Identify the threshold value
3. Using the index in #1, find the index of the first value that is <=threshold value starting at the peak. To get its index in the full WF data, you will need to add the index from #1 to the result. Something like this might work (untested)

ind = find(resampled_WF(indPk:end)<=WF_threshold_input,1) + indPk-1;