How can i find the norm error btw a function and a summation?

Hello! i wanna do this summation with some sample x's.

x_j's are givin int he formula amd they change in the summation acording to summation index.

x is an unknown in the summation but i have to assign a vector to x and this vector should be like this x=0:2pi/100:2pi and my summation have to be a vector at the end(or it have not be im not sure)

Also i have to calculate u(x) (e.g. u(x)=x )for the same x values. Cause at the end i will calculate the norm of the error |Summation-u(x)| at this sample x points an draw x vs this norm graph.

Can someone help me please?

Thanks!!

Here is my code i think formulation is correct bu i dont know how to insert x values in to the code

 clc

 clear all

 f= @(x) x;

 N=4;

 x_d=0:2*pi/100:2;

 for j=0:N  

 x_j(j+1,1)=(2*pi*j)/(N+1); 

 I(j+1,1)=f(x_j)*sin((N+1)*(x_d-x_j)/2)/sin((x_d-x_j)/2);

 end

 I_n=(1/(N+1))*sum(f(:,1));

(x_d are sample points)