Finding maxima in blocks of data, consecutively

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Josh Carmichael
Josh Carmichael 2013-5-16
Problem Statement: I have a time series, x. I am interested in consecutive, temporal blocks of x where x > value. I also want to focus on blocks that are at least time "T" apart. Let x(*) indicate x at time index *. If:
x(m-K), x(m-K+1), x(m-K+2), ...x(m) > value
and, later at n > m + T (a greater time)
x(n-K), x(n-K+1), x(n-K+2), ...x(n) > value
I want to identify the maximal value within each block, while ignoring all temporally consecutive blocks that are less than T samples apart. I currently have a for loops-method that works, but it's clumsy and not great for the application I have in mind.
Application: I am trying to detect certain events, where x exceeds a detection statistic, but I only want events spaced "T" distance apart. Events closer than "T" are considered to be the same.
HELP? Thanks.

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Image Analyst
Image Analyst 2013-5-16
Can't you just say
maxValue = max(x(n-K:n));
or similar for m? If you have the Image Processing Toolbox, you can use imdilate(), which is a sliding local maximum. If you want to get the max only of x with values greater than value, then
thresholdedX = x(x>value);
but then I'm not sure if the (n-K) and n apply to the indexes before or after thresholding and extraction of the values above the threshold value, so I can't give the next step for certain.
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Image Analyst
Image Analyst 2013-5-16
Do you have the Image Processing Toolbox? If so you can do this easily. Just threshold and mask and pass to imdilate, then mask again. It's like 4 lines of code.
Josh Carmichael
Josh Carmichael 2013-5-16
Thanks for the note! I don't have an image processing toolbox, just the statistics and signal processing box, as I said above. But, maybe I can look up the imdilate code. Thanks again!

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