# Plotting the integral of a graph

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Hans123 on 4 Dec 2019
Commented: Fabio Freschi on 4 Dec 2019
Hi,
I have a graph of a waveform that I want to find the integral plot of this waveform (shown below). Could this be done on MATLAB or is this something for Simulink. I am new to Simulink, and I would appreciate any help on graphing the integral plot. Fabio Freschi on 4 Dec 2019
Suppose that x and y are the vectors defining your waveform.
% dummy values
x = linspace(0,2*pi,1000);
y = sin(x);
% integral
Y = cumtrapz(x,y);
% plot
figure, hold on
plot(x,y); % waveform
plot(x,Y); % integral
legend('waveform','integral')

Hans123 on 4 Dec 2019
thank you Fabio! I just want to verify the plot I got is the integral - what would be the code to derive Y so I could plot it and verify it is the same as the initial plot.
Fabio Freschi on 4 Dec 2019
My pleasure! The derivative can be obtained with diff function.
yd = diff(Y)./diff(x);
% yd has one point less, so we must calculate an ad-hoc x vector
xd = (x(1:end-1)+x(2:end))/2;
% plot
plot(xd,yd);