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

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.

Answer 1

[Image Analyst]

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

[Kimberly Cardillo]

This is not for homework. it is for my research. This code will create a cell array with all the values just below and just above y=10?

[Image Analyst]

It creates a cell array with the elements (indexes) right before where the signal crosses from

1. below 10 to above 10, and
2. above 10 to below 10

So you'd take those indexes and add 1 to get the index right after they crossed 10 - in other words on the other side. Then do a simple blinear interpolation to get the interpolated values at exactly 10. You can do that part, right?

[Kimberly Cardillo]

Yeah, I think I can do the interpolation from there. What is the 44 for in the first line?

[Kimberly Cardillo]

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

[Image Analyst]

You forgot to attach your script and data (aefm_4), so how can we debug your program for you???