# How to plot results from Simpson's Rule integration?

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aw007 on 15 Oct 2020
Commented: aw007 on 15 Oct 2020
Hi All,
I am currently trying to do some integration using the Simpson's rule. My codes does produce the required approximation. But I don't understand how I can obtain a plot of the number of panels (x-axis) vs the integral evaluated at each panel (y-axis). My code uses 10 panels. The plot should be some what of a zig zag in appearance. Could someone please provide some assistance regarding this matter?
My code is shown below:
%Function to be integrated
f=@(x)exp(x);
%lower limit
a=0;
%upper limit
b=1;
%number of panels
n=10;
%interval size
h=(b-a)/n;
%summation of first two values
s=f(a)+f(b);
%loop for the rest of the calculations
for i=1:2:n-1
s=s+4*f(a+i*h); %summation
end
for i=2:2:n-2
s=s+2*f(a+i*h); %summation
end
%evaluate integral
I=h/3*s

%Function to be integrated
f=@(x)exp(x);
%lower limit
a=0;
%upper limit
b=1;
N=[10, 20, 40, 100, 200, 400, 800, 1000];
In = NaN(size(N));
%number of panels
for j = 1:length(N)
%interval size
n=N(j);
h=(b-a)/n;
%summation of first two values
s=f(a)+f(b);
%loop for the rest of the calculations
for i=1:2:n-1
s=s+4*f(a+i*h); %summation
end
for i=2:2:n-2
s=s+2*f(a+i*h); %summation
end
%evaluate integral
I=h/3*s;
In(j) = I;
end
% plot(N,In);
% or
semilogx(N,In);
end
aw007 on 15 Oct 2020
Thanks for the help Asad, after a brief modification of your code I managed to get the correct result for my purpose.

R2020a

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