Having trouble to calculate the area under curve for each peaks and display the area under curve in graph?
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Keshasni Earichappan
on 10 Aug 2021
Commented: Star Strider
on 11 Aug 2021
Hi there.I am new to mathlab and having trouble to calculate the area under curve for each peaks and display the area under curve in graph? i have attached the file over here.Hope someone can help me. thanks in advance.
2 Comments
Scott MacKenzie
on 10 Aug 2021
It's not clear what you are trying to do; i.e, what precisely do you mean by "peak"? Running your data through findpeaks indicates 18,015 peaks. With some smoothing... Well, let me just illustrate my point as follows:
f = 'https://www.mathworks.com/matlabcentral/answers/uploaded_files/708072/time%20vs%20Muscle%20contraction.txt';
M = readmatrix(f);
x = M(:,1);
y = M(:,2);
tiledlayout('flow');
nexttile;
plot(x,y);
nexttile;
y2 = smoothdata(y);
plot(x,y2);
[pks, loc] = findpeaks(y);
[pks2, loc2] = findpeaks(y2);
[length(pks) length(pks2)]
Accepted Answer
Star Strider
on 10 Aug 2021
It depends entirely on what the definition of ‘peak’ is, and if the data first need to be detrended.
T1 = readtable('https://www.mathworks.com/matlabcentral/answers/uploaded_files/708072/time%20vs%20Muscle%20contraction.txt', 'VariableNamingRule','preserve')
t = T1.TIME;
v = T1.('MC[v]');
Ts = mean(diff(t),'omitnan');
Fs = 1/Ts;
Fn = Fs/2;
figure
plot(t, v)
grid
xlabel('t')
ylabel('v')
title('Original Data')
vfilt = highpass(v, 1E-4, Fs, 'ImpulseResponse','iir');
zxi = find(diff(sign(vfilt)));
for k = 1:numel(zxi)
idxrng = max(1, zxi(k)-1) : min(numel(v),zxi(k)+1);
tzc(k) = interp1(vfilt(idxrng),t(idxrng),0);
end
tzc = unique(tzc);
for k = 1:numel(tzc)-1
Lv = (t>=tzc(k) & t<=tzc(k+1));
tv{k} = t(Lv);
vv{k} = vfilt(Lv);
if (numel(vv{k}) > 1)
Area(k) = trapz(tv{k},vv{k});
else
Area(k) = 0;
end
tvm(k) = mean(tv{k});
maxvv = max(vv{k});
if (~isempty(maxvv))
pkv(k) = maxvv;
else
pkv(k) = NaN;
end
end
figure
plot(t, vfilt)
hold on
plot(tzc, zeros(size(tzc)), 'xr')
hold off
grid
xlabel('t')
ylabel('v')
title('Original Data (Detrended)')
legend('Data', 'Zero-Crossings', 'Location','best')
% text(tvm,pkv, compose('\\leftarrow %.3f',Area), 'Horiz','center', 'Vert','bottom', 'Rotation',90)
.
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