Continuing Matrix involving a function to make very large

Hi all, i have a typed square matrix and need to expand it to be very large how ever this will take far too long to do manually. my matrix code is below please help if you know any function to expend it while keeping the same pattern.

thanks in advance

syms e P n
c=1;
G(n)=e/(2*(P+0.5*(1i*n*c)-(0.25*(n)^2)));
j=[1 0 G(7) 0 0 0 0 0 0 0 0 0 0 0 0;0 1 0 G(6) 0 0 0 0 0 0 0 0 0 0 0; G(5) 0 1 0 G(5) 0 0 0 0 0 0 0 0 0 0; 0 G(4) 0 1 0 G(4) 0 0 0 0 0 0 0 0 0; 0 0 G(3) 0 1 0 G(3) 0 0 0 0 0 0 0 0; 0 0 0 G(2) 0 1 0 G(2) 0 0 0 0 0 0 0; 0 0 0 0 G(1) 0 1 0 G(1) 0 0 0 0 0 0 ; 0 0 0 0 0 G(0) 0 1 0 G(0) 0 0 0 0 0; 0 0 0 0 0 0 G(-1) 0 1 0 G(-1) 0 0 0 0; 0 0 0 0 0 0 0 G(-2) 0 1 0 G(-2) 0 0 0; 0 0 0 0 0 0 0 0 G(-3) 0 1 0 G(-3) 0 0; 0 0 0 0 0 0 0 0 0 G(-4) 0 1 0 G(-4) 0; 0 0 0 0 0 0 0 0 0 0 G(-5) 0 1 0 G(-5); 0 0 0 0 0 0 0 0 0 0 0 G(-6) 0 1 0; 0 0 0 0 0 0 0 0 0 0 0 0 G(-7) 0 1 ];

[KSSV]

'P' not defined.

[KSSV]

Read about diag.

Answer 1

[Ameer Hamza]

Try this

syms e o n
c=1;
P = 1;
G(n)=e./(2.*(P+0.5*(1i*n.*c)-(0.25*(n)^2)));

N = 15;
l_start = 5;
u_start = 7;
l_end = l_start-N+3;
u_end = u_start-N+3;

j = diag(ones(1,N)) + diag(G(l_start:-1:l_end), -2) + diag(G(u_start:-1:u_end), 2);