Determine the start and end of a vector.

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Ferd 2016-9-27

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评论： Ferd 2016-9-28

When the variable starts incrementing above a threshold, that index is to be determined and also when the same variable starts decrementing below a certain threshold, the index is to be determined.

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Walter Roberson 2016-9-27

Are the two thresholds the same value?

Ferd 2016-9-28

Two different thresholds

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Answer 1

Image Analyst 2016-9-28

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Try using diff() and strfind():

% Create random sample data.
v = randi(9, 1, 20)
thresh = 3; % Define the threshold.
% Find indexes where v is at or above the threshold.
d = (v>=thresh)
% Find the starting index where the signal starts above the threshold
% and then starts to fall below the threshold.
fallsBelow = strfind(d, [1, 0])
% Find the starting index where the signal starts below the threshold
% and then starts to rise above the threshold.
risesAbove = strfind(d, [0, 1])

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Walter Roberson 2016-9-28

This is a good approach when the thresholds are the same. Matters get more complicated when the thresholds are different. For example if you wanted to trigger at 1/4 Volt and to keep monitoring until you dropped to 0 V, then it becomes trickier.

Ferd 2016-9-28