savitzky golay derivation graph plot

Question

Alexai 2022-12-15

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评论： Alexai 2022-12-29

I want to draw a first differential graph and a second differential graph using savitzky golay in the Matlab plot, which code should I use?

Here's an example of a code. x1=[1 2 3 4 5]; x2=[1 5 2 9 4]; x3=[3 2 1 6 4]; y=[500 505 510 515 520]; %this is wavelength plot (y, x1) hold on plot (y, x2) hold on plot (y, x3) I'm going to plot three graphs(x1,x2,x3)

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Answer 1

Sai Kiran 2022-12-23

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Hi,

I understand that you want to calculate the first & second differential using the Savitzky-Golay filter. This can be calculated by the 'sgolayfilt' function.

sgolayfilt(x,order,framelen) where x is an array on which we perform the differential and framelen is the size of the x.

Please refer to the below documentation for more information on sgolayfilt function.

sgolayfilt_documentation

% Load the signal to be filtered
x1 = [1 2 3 4 5];
x2 = [1 5 2 9 4];
x3 = [3 2 1 6 4];
y = [500 505 510 515 520]; % this is the wavelength
% Compute the first derivative of each signal using the Savitzky-Golay filter
dx1 = sgolayfilt(x1, 1, 5);
dx2 = sgolayfilt(x2, 1, 5);
dx3 = sgolayfilt(x3, 1, 5);
% Plot the first derivative of each signal
figure;
plot(y, dx1);
hold on;
plot(y, dx2);
plot(y, dx3);
xlabel('Wavelength');
ylabel('First derivative');
legend('x1', 'x2', 'x3');
% Compute the second derivative of each signal using the Savitzky-Golay filter
ddx1 = sgolayfilt(x1, 2, 5);
ddx2 = sgolayfilt(x2, 2, 5 );
ddx3 = sgolayfilt(x3, 2, 5);
% Plot the second derivative of each signal
figure;
plot(y, ddx1);
hold on;
plot(y, ddx2);
plot(y, ddx3);
xlabel('Wavelength');
ylabel('Second derivative');
legend('x1', 'x2', 'x3');