Having trouble to calculate the area under curve for each peaks and display the area under curve in graph?

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.

[Scott MacKenzie]

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)]

ans = 1×2

18015 363

[Keshasni Earichappan]

Hi Scott MacKenzie.Thank you for answering.The 'peak' i mentioned is a SIGNAL PEAK(SP) .Basically, i need to know how to calculate the area under curve for each muscle contractions( MC[V] ) and plot them as a graph.

Answer 1

[Star Strider]

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')

T1 = 90483×2 table
    TIME    MC[v] 
    ____    ______

    NaN     1.8297
      0     1.8289
     10     1.8297
     20     1.8297
     30     1.8305
     40     1.8289
     50     1.8297
     60     1.8313
     70     1.8305
     80     1.8281
     90     1.8297
    100     1.8305
    110     1.8305
    120     1.8297
    130     1.8297
    140     1.8305

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)

.

[Keshasni Earichappan]

Hi Star Strider..thank you for answering..i have tried this and it's worked perfectly.Thank you so much.:)

[Star Strider]

As always, my pleasure!

.