how can i find the start points and end points of the segment of a plot when the plot is below a certain tolerance in matlab

To find the start and end points of a segment of a plot that is below a certain tolerance in MATLAB, you can use the find function along with logical indexing.

Firstly, plot the data and determine the tolerance value below which you want to detect the segments. Then, get the indices of the values that are below the tolerance using find function.

Next, you can use diff function to find the indexes where the values transition from being below the tolerance to above it and vice versa. diff calculates the differences between consecutive elements of an array. If two consecutive values are of opposite signs, this indicates a transition from below tolerance to above tolerance or vice versa.

Finally, use these transition indexes to get the start and end points of each segment. Here is the sample code:

main.m
% Generate some test data
x = linspace(0, 10, 100);
y = sin(x);

% Set the tolerance
tolerance = 0.2;

% Find the indices of the values below the tolerance
below_tolerance = find(abs(y) < tolerance);

% Find the indexes of the transitions from below to above tolerance
diffs = diff(below_tolerance > 0);
starts = find(diffs == 1) + 1;
ends = find(diffs == -1);

% Plot the original data
plot(x, y); hold on;

% Plot the detected segments
for ii = 1:length(starts)
   segment_x = x(starts(ii):ends(ii));
   segment_y = y(starts(ii):ends(ii));
   plot(segment_x, segment_y, 'r', 'LineWidth', 2);
end

% Add labels and title
xlabel('x-axis');
ylabel('y-axis');
title('Segments below tolerance');
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This will plot the original data and then plot the segments that are below tolerance in red color. The start and end points of each segment are calculated using the find and diff functions.