Creating cell array for values in a signal vector that cross a certain threshold

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Kimberly Cardillo 2020-10-13

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评论： Image Analyst 2020-10-14

I have a 1599 x 54 double matrix called aefm_4 were the columns represent observations (signals) and the rows represent time steps. For each column, I want to find the row number where the value is equal to 10. For example, I have a signal (whose signal vector is a certain column number in the matrix) as seen in the picture below and I want to find the x values (row number) of where the threshold (red line) and signal (blue line) cross. Not every signal will cross this threshold exactly 10 times, thats why I want to make it a cell array. Also, the y values wont be at exactly y=10 so i need to find the values directly above and below y=10 and then interpolate. If anyone could help me with this or at least get me started, that would be great.

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Answer 1

Image Analyst 2020-10-13

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https://ww2.mathworks.cn/matlabcentral/answers/612931-creating-cell-array-for-values-in-a-signal-vector-that-cross-a-certain-threshold#answer_513061

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Is this homework?

Here's a start. It gives you the elements just before where it crosses 10. Take the element after and do a blinear interpolation with interp1. I trust you can do that but let us know if you can't figure it out after a good attempt.

data = 100 * rand(1599, 44) - 50;
[rows, columns] = size(data);
for col = 1 : columns
	thisColumn = data(:, col);
	plot(thisColumn, 'b-');
	% Draw threshold.
	yline(10, 'Color', 'r', 'LineWidth', 2);
	% Draw y axis.
	yline(0, 'Color', 'k', 'LineWidth', 2);
	drawnow;
	risingIndexes{col} = strfind(thisColumn' > 10, [0, 1]);
	fallingIndexes{col} = strfind(thisColumn' > 10, [1, 0]);
end

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Kimberly Cardillo 2020-10-14

I ran the code with data = aefm_4; and i get the error, unable to perform assignment because brace indexing is not supported for variables of this type