Input on making a matrix?

I have very little knowledge about Matlab and need some input. Here is my code. I keep getting an error on line 27. Index exceed the number of array elements. I understand a little bit on why im getting this error, but I do not know how to fix it.

L = 1;      %m
a = 0.001;  %m
VO = 1.0;   %V
Eo = 8.8541e-12; 
N = 5 ; % number of segments
d = 0.05; %m
Delta = L/N;
 
prompt ='Enter the value for d  ';
d = input (prompt)
 
 
% Matrix A
y = Delta/2:Delta:L-Delta/2;
 
 
  B=N*2;
  c=N*2;
    
    
A = zeros(B,c);
for n = (1:N)*2
    for m = (1:N)*2
        if m == n
            A(n,n) = 2*log(Delta/a);
        else
            A(n,m) = Delta/abs(y(m)-y(n));
             if n==m
            A(n,n) = 2*log(Delta/sqrt((y(n)-y(m))^2+(d)^2));
        else
            A(n,m) = Delta/abs(y(m)-y(n));
             end
        end
    end
end
 
    disp(n);
    
    
 
disp(m);
 
   
 
disp(A);
 
 
% Vector B
b = 4*pi*Eo*(VO/2)*[-ones(1,N) ones(1,N)].';
 
%rho = inv(A)*b;
rho = A\b;
 
% Capacitance calculation
Ql = sum(rho([1:N]))*Delta;
 
Qu = sum(rho([N+1:2*N]))*Delta;
 
C = Qu/VO; 
 
disp(C);
 
 
%figure (1), clf;
%plot(y,rho,'*--'); grid on;
 
 
%Plot rho against Y 
xlabel('y_n');
ylabel('Charge Density (C/m');
title ('Calculation of Charge Density');
 

[Abhishek Gangwar]

You are getting this error because y is a 1x5 row vector and the index values (n, m) in nested loops are all even numbers [2, 10], try to modify your code.

Answer 1

[KSSV]

Size of y is 1*N where as size of A is 2N*2N. You need to increase the size of y. You can replace y with:

y = linspace(Delta/2,L-Delta/2,2*N) ; 

[Tristan McCarver]

Thank you for the help! I no longer get the error. I do have another question though. When I run the code I can populate a 5X5 matrix but the rest are 0 in the 10X10 matrix of A. How do I increase n and m to fill up the rest of the matrix?

[Tristan McCarver]

Ok I believe I have figured that out. The plot is suppose to look like a parabola it is coming out wrong.

[Tristan McCarver]

Here is what im trying to make my A matrix look like.