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

I want to calculate knee point of a curve in existing software through 2nd derivative. Can anyone help to create script.

Answer 1

[Star Strider]

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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