concurrence calculation of qubit system

I need to calcualte the concurrenec for the given density matrix. Pl somebody see my code and solve my issue.

clc
close all

function c=concurrence(rho)
rho=1/2*[0 0 0 0;0 1 -1 0;0 -1 1 0;0 0 0 0];
 y=[0 -1i; 1i 0];          
 R=rho*kron(y,y)*conj(rho)*kron(y,y);
 % Real is needed since MATLAB always adds a small imaginary part ...
 e=real(sqrt(eig(R)));
 e=-sort(-e);
 c=max(e(1)-e(2)-e(3)-e(4),0)
end

The concurrenec is not coming. Pl help me to get that.

[Mohammad Sami]

What seems to be the problem ?

Answer 1

[Ibrahim Issah]

%% intialize %%

clc

close all

clear

%%%%%%%%%%%%%

%% density matrix%%%%

rho=1/2*[0 0 0 0;0 1 -1 0;0 -1 1 0;0 0 0 0];

%%%%%%% pauli matrix%%%%%%%%%%

y=[0 -1i; 1i 0];

%%% p and ptilda %%%%%%%

R=rho*kron(y,y)*conj(rho)*kron(y,y);

% Real is needed since MATLAB always adds a small imaginary part ...

e=real(sqrt(eig(R)));

e=-sort(-e);

c=max(e(1)-e(2)-e(3)-e(4),0);

disp(c);

%% Apparently you don't need any function for this since your density matrix is already defined. Thank you.