Find the difference between positive and negative peaks MATLAB - matlab

Question

I need to find the difference between positive and negative peaks where the difference is greater than +-3.
I am using findpeaks function in MATLAB to find the positive and negative peaks of the data.
In an example of my code:
[Ypos, Yposloc] = findpeaks(YT0);
[Yneg, Ynegloc] = findpeaks(YT0*-1);
Yneg = Yneg*-1;
Yposloc and Ynegloc return the locations of the positive and negative peaks in the data.
I want to concatenate Ypos and Yneg based on the order of the peaks.
For example, my peaks are
Ypos = [11 6 -10 -10 6 6 6 6 6 -5]
Yneg = [-12 -14 -11 -11 -11 5 5 5 -6]
Locations in YT0
Yposloc = [24 63 79 84 93 95 97 100 156]
Ynegloc = [11 51 78 81 85 94 96 99 154]
In this case, where both Yposloc and Ynegloc are 9x1, I can do the following;
nColumns = size(Yposs,2);
YTT0 = [Yneg, Ypos]';
YTT0 = reshape(YTT0(:),nColumns,[])';
YTT0 = diff(YTT0)
YT0Change = numel(YTT0(YTT0(:)>=3 | YTT0(:)<=-3));
Total changes that I am interested is 6
However, I need to concatenate Yneg and Ypos automatically, based on their locations. So I think I need to to do an if statement to figure out if my positive or negative peaks come first? Then, I am not sure how to tackle the problem of when Ypos and Yneg are different sizes.
I am running this script multiple times where data changes and the negative/positive peak order are constantly changing. Is there a simple way I can compare the peak locations or am I on the right track here?

Answer 1

I would check each minimum with both the previous and the next maxima. In order to do that you can first combine positive and negative peaks according to their order:
Y = zeros(1, max([Yposloc, Ynegloc]));
Yloc = zeros(size(Y));
Yloc(Yposloc) = Yposloc;
Yloc(Ynegloc) = Ynegloc;
Y(Yposloc) = Ypos; % I think you inserted one extra '6' in your code!
Y(Ynegloc) = Yneg;
Y = Y(Yloc ~= 0) % this is the combined signal
Yloc = Yloc(Yloc ~= 0) % this is the combined locations
% Y =
%
% -12 11 -14 6 -11 -10 -11 -10 -11 6 5 6 5 6 5 6 -6 -5
%
% Yloc =
%
% 11 24 51 63 78 79 81 84 85 93 94 95 96 97 99 100 154 156
And then calculate the differences:
diff(Y)
% ans =
%
% 23 -25 20 -17 1 -1 1 -1 17 -1 1 -1 1 -1 1 -12 1
If you want changes of at least 6 units:
num = sum(abs(diff(Y)) > 6)
% num =
%
% 6

Answer 2

Ypos = [11 6 -10 -10 6 6 6 6 -5];
Yneg = [-12 -14 -11 -11 -11 5 5 5 -6];
Yposloc = [24 63 79 84 93 95 97 100 156];
Ynegloc = [11 51 78 81 85 94 96 99 154];
TOTAL=[Yposloc Ynegloc;Ypos Yneg];
%creatin a vector with positions in row 1 and values in row 2
[~,position]=sort(TOTAL(1,:));
%resort this matrix so the values are in the orginial order
TOTAL_sorted=TOTAL(:,position);
%look at the changes of the values
changes=diff(TOTAL_sorted(2,:));
if changes(1)>0
disp('First value was a Minimum')
else
disp('First value was a MAximum')
end
%same structure at the TOTAL matrix
%abs(changes)>3 produces a logical vector that shows where the absolute values was bigger
%than 3, in my opinon its rather intresting where the end is then were the start is
% thats why i add +1
Important_changes=TOTAL_sorted(:,find(abs(changes)>3)+1);
plot(TOTAL_sorted(1,:),TOTAL_sorted(2,:))
hold on
plot(Important_changes(1,:),Important_changes(2,:),...
'Marker','o','MarkerSize',10, 'LineStyle','none');
hold off