Hi, I want to know knee point of a curve including the process of by 2nd derivative. Can anyone help by creating the script.

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DIPESH THAWANI
DIPESH THAWANI on 16 Oct 2021
Edited: Star Strider on 16 Oct 2021
I want to calculate knee point of a curve in existing software through 2nd derivative. Can anyone help to create script.

Answers (1)

Star Strider
Star Strider on 16 Oct 2021
Edited: Star Strider on 16 Oct 2021
Use the gradient function to calculate the numerical derivative —
x = linspace(0, 10);
y = exp(-0.1*x) .* sin(x);
D1 = gradient(y) ./ gradient(x);
D2 = gradient(D1) ./ gradient(x);
figure
plot(x, y, x, D1, x, D2)
grid
legend('$y(x)$', '$\frac{dy}{dx}$', '$\frac{d^2y}{dx^2}$', 'Location','best', 'Interpreter','latex')
EDIT — (16 Oct 2021 at 21:22)
I am not certain what the curve is. Additional options (includeing the derivative approach) could be findchangepts or ischange.
.

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