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 2021-8-10

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https://ww2.mathworks.cn/matlabcentral/answers/895677-having-trouble-to-calculate-the-area-under-curve-for-each-peaks-and-display-the-area-under-curve-in

评论： Star Strider 2021-8-11

time vs Muscle contraction.txt

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.

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Scott MacKenzie 2021-8-10

在 MATLAB Online 中打开

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 2021-8-10

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.

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Answer 1

Star Strider 2021-8-10

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/895677-having-trouble-to-calculate-the-area-under-curve-for-each-peaks-and-display-the-area-under-curve-in#answer_764267

在 MATLAB Online 中打开

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

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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Keshasni Earichappan 2021-8-11

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

Star Strider 2021-8-11

As always, my pleasure!

.

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