During calculations , a constant is obtained instead of a function

I have a complex function that depends on 'd' and 'n' F(n,d) I need to sum a series over 'n' and plot F(d).

I know that after summing by 'n' I should get a function F(d) which is rapidly oscillating and decaying. But after summing, I get a constant that does not depend on d.

My cod:

%% initial conditions

global t k0 h_bar ksi m E;

Ef = 2.77*10^3;

Kb = physconst('boltzmann'); % 1.38*10^(-23)

D = 5:5.1:50;

m = 9.1093837*10^(-31);

Tc = 1.2;

t = 1;

ksi = 10^(-9);

d = D./ksi;

E = Ef/(pi*Kb*Tc);

h_bar = (1.0545726*10^(-34));

k0 = (ksi/h_bar)*sqrt(2.*m.*pi.*Kb.*Tc);

C_2 = 0;

for n = 0:49

C_2 = C_2 + (1/(2.*n+1)).*k0.*real(sqrt(E+1i.*(2.*n+1))-((1+1i)./sqrt(2)).*sqrt(2.*n+1)); % константа

end

%% calculation

F = f_calc(d);

plot(d,F,'o');

%% F(d)

function F = f_calc(d)

global t k0 h_bar ksi m;

F = 0;

for n = 0:49

F = F + 1/(2*n+1).*imag(f_lg(n,t)+1i*d.*k0.*((f_p1(n)-f_p2(n))./2)+1i*f_arg_1(n,d)-1i*f_arg_2(n,d));

end

F = -(1./d).*F;

plot(d,F,'o');

end

function p1 = f_p1(n)

global t;

p1 = ((1+1i)./sqrt(2)).*sqrt(t.*(2.*n+1));

end

function p2 = f_p2(n)

global t E;

p2 = sqrt(E+1i.*t.*(2.*n+1));

end

function n_lg = f_lg(n,d)

global t k0;

arg_of_lg = (1+exp(-1i*d*k0.*f_p1(n)))/(1+exp(-1i*d*k0.*f_p2(n)));

n_lg = log(abs(arg_of_lg));

end

function arg_1 = f_arg_1(n,d)

global t k0;

arg_1 = angle(1+exp(-1i*d*k0.*f_p1(n)));

end

function arg_2 = f_arg_2(n,d)

global t k0;

arg_2 = angle(1+exp(-1i*d*k0.*f_p2(n)));

end

[Torsten]

But after summing, I get a constant that does not depend on d.

You get a vector of values that depends on d. But the difference between its elements is very small compared to their absolute value (1e11).