How can I calculate three different shaded areas?

I have three groups of sample points as attached, and intend to calculate three different shaded areas under curve from x = -40 to x = 30 by using for loop.

Answer 1

[Star Strider]

Try this —

T1 = readtable('example.xlsx')

T1 = 6171x6 table
      x1         y1        x2         y2        x3         y3  
    _______    ______    _______    ______    _______    ______

    -69.644    10.562    -69.643    10.583    -69.631    10.605
    -69.641    10.574    -69.641    10.596    -69.629    10.618
    -69.639    10.586    -69.639    10.608    -69.626    10.631
    -69.636    10.599    -69.636    10.621    -69.624    10.644
    -69.634    10.611    -69.634    10.633    -69.622    10.657
    -69.632    10.623    -69.632    10.645    -69.619     10.67
    -69.629    10.636    -69.629    10.658    -69.617    10.683
    -69.627    10.648    -69.627     10.67    -69.614    10.696
    -69.625     10.66    -69.625    10.682    -69.612    10.709
    -69.622    10.673    -69.622    10.694    -69.609    10.721
     -69.62    10.685     -69.62    10.707    -69.607    10.734
    -69.615     10.71    -69.615    10.732    -69.602    10.758
     -69.61    10.734     -69.61    10.758    -69.597    10.783
    -69.606    10.759    -69.605    10.784    -69.593    10.807
    -69.601    10.784      -69.6     10.81    -69.588    10.831
    -69.596    10.809    -69.595    10.836    -69.583    10.856

for k = 1:2:size(T1,2)
    xv = T1{:,k};
    yv = T1{:,k+1};
    idxrng = (xv >= -40) & (xv <= 30);
    AUC(ceil(k/2)) = trapz(xv(idxrng), yv(idxrng));
end

AUC

AUC = 1×3

98.2744 90.7472 80.9077

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figure
tiledlayout(3,1)
for k = 1:2:size(T1,2)
    % k
    xv = T1{:,k};
    yv = T1{:,k+1};
    nexttile
    plot(xv, yv)
    hold on
    idxrng = (xv >= -40) & (xv <= 30);
    patch([xv(idxrng); flip(xv(idxrng))], [zeros(nnz(idxrng),1); flip(yv(idxrng))], 'r', 'FaceAlpha',0.5)
    hold off
    grid
end

.

[wd w]

Star Strider, thank you very much!

[Star Strider]

As always, my pleasure!