# How can i found the infelction point from the data and remove the data before the first and last infelction points.

1 view (last 30 days)
JINU SUDHAKARAN Mr on 16 Jan 2023
Commented: Star Strider on 27 Jan 2023
I need to find the inflection point from the experimental data using matlab. Kindly help me for that. Thanks in advance

Star Strider on 16 Jan 2023
The data are quite noisy. After filtering them, it is not obvious what sort of inflection point you want or how to define it.
M1 = 1430×2
0 32.2683 0.0050 32.2683 0.0100 32.2683 0.0150 32.2683 0.0200 32.2683 0.0250 32.2683 0.0300 32.2683 0.0350 32.2683 0.0400 32.2683 0.0450 32.2683
x = M1(:,1);
y = M1(:,2);
% yf = sgolayfilt(y, 3, 451);
Fs = 1/mean(diff(x))
Fs = 200
Fn = Fs/2;
L = numel(x);
NFFT = 2^nextpow2(L);
FTy = fft((y-mean(y)).*hann(L),NFFT)/L;
Fv = linspace(0, 1, NFFT/2+1)*Fn;
Iv = 1:numel(Fv);
figure
semilogy(Fv, abs(FTy(Iv))*2)
grid
xlim([0 10]) yf = lowpass(y, 0.5, Fs, 'ImpulseResponse','iir');
figure
yyaxis left
plot(x, y, 'DisplayName','Unfiltered Data')
hold on
plot(x, yf, '-r', 'DisplayName','Filtered Data')
hold off
ylabel('Data')
yyaxis right
plot(x, dyfdx, 'DisplayName','First Derivative Of Filtered Data')
hold on
plot(x, d2yfdx2, 'DisplayName','Second Derivative Of Filtered Data')
hold off
yline(0, '-g')
ylabel('Derivatives')
grid
legend('Location','best') .
Star Strider on 27 Jan 2023
My pleasure!
.

Steven Lord on 16 Jan 2023
The ischange, islocalmin, and/or islocalmax functions may be of use to you, as might the corresponding Live Editor Tasks Find Change Points and Find Local Extrema.