Eliminating noise in a vibration analysis study

I have accelerometer data for an underdamped system and I need to delete everything before the max deflection. Does anybody know how I can find which vector element the max is and then delete everything above it.

For example: b = [.3;.2;.34;12;10;7]

And I need to know that the max is 12 and create another vector that is bb = [12;10;7] but with many more vector elements.

Can anyone help me out?

Answer 1

[Image Analyst]

Liza: Try this:

% Find the max value and where it's located.
[mavValue, indexOfMaxValue] = max(b);
% Extract elements after the index of the max:
bb = b(indexOfMaxValue : end);

I really suggest you use more descriptive variable names than b and bb, like I did above for the new variables. I wouldn't want your code to look like an un-maintainable alphabet soup of code that's a total mess.

Your plot is slightly different since there's a very large value that's not quite as tall as the max. If you want that you need to threshold

indexOfMaxValue = find(b>2, 1, 'first');
% Extract elements after the index of the first value greater than 2:
bb = b(indexOfMaxValue : end);

[Image Analyst]

Liza's answer moved from an Answer to a comment here:

This is awesome. Thank you so much! And thanks for the tip