MATLAB: How to integrate area under peak

area under peak

For my events, I have data points for y-axis. As a sample, I have attached a text file containing datapoints for one of my events. As I have shown in figure, I want to integrate area of each region displayed in various colors. I can find start and end boundary for a region using findchangepts function. However, it provides start and end points few points away from the exact location. Could you please help me with this? Also, if someone can suggest any other function to find start and end boundary, would be a great help.

I have tried, trapz(y); but didn't work the way I want.

Best Answer

Try this:

D = load('data for peak area.txt');
idx = D >= 0.28;
chg = [find(diff(idx ~= 0)); numel(D)];
chg(1) = 1;
for k1 = 1:numel(chg)-1
    segment_area(k1) = trapz(chg(k1:k1+1), D(chg(k1:k1+1)));
    Q1(:,k1) = chg([k1 k1+1]);
    Q2(:,k1) = D(chg([k1 k1+1]));
end
figure(1)
plot(D)
hold on
plot(Q1, Q2, 'pg')
hold off
grid
area_text = regexp(sprintf('%.2f\n', segment_area), '\n', 'split');
text(mean(Q1), ones(size(segment_area))*0.12, area_text(1:end-1), 'HorizontalAlignment','center')

Related Solutions

MATLAB: How to calculate area under each peak from the plot

See if this does what you want:

D = load('data for plot.txt');
x = 0:numel(D)-1;                                               % Choose The Appropriate Vector For The Most Accurate Results
[pks,locs] = findpeaks(-D);                                     % ‘Trough’ Minima Between Peaks
IntTot = cumtrapz(x,D);                                         % Integrate
IntPks = diff(IntTot(locs));                                    % Peak Areas
IntPks =
        0.45474
        0.08047
        0.15185
        0.20436
        0.25881
      0.0068099

MATLAB: Getting the area under the peaks

I would first identify the low points (‘valleys’) by inverting your signal and then using the Signal Processing Toolbox findpeaks function to locate them. Then integrate between those points to identify the peaks.

Example —

t = linspace(0, 10*pi, 250);                        % Create Data

s = sin(t) + 0.2*cos(5*t) + 2;                      % Create Data
figure(1)
plot(t, -s)
grid
[Vlys, Idx] = findpeaks(-s, 'MinPeakHeight',-1.1);
Area = cumtrapz(t,s);
idxvct = [1 Idx length(s)];
for k1 = 1:length(idxvct)-1
    PkAreas(k1) = Area(idxvct(k1+1)) - Area(idxvct(k1));
end

The ‘PkAreas’ vector will have the areas of the peaks.

You will have to adapt this to your data. Be sure to plot the negative of your data first so you can see and set the appropriate arguments for findpeaks.

Best Answer

Related Solutions

MATLAB: How to calculate area under each peak from the plot

MATLAB: Getting the area under the peaks

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