function [E F D] = Expression(K,Con)
 
%%
% user supplies the input concentration list, assign the concentration value 
A = Con(1);
B = Con(2);
C = Con(3);
P = Con(4);
 
%%
% user supplies the input parameter K, assigning the value to k
k1 = K(1);
k2 = K(2);
k3 = K(3);
k4 = K(4);
k5 = K(5);
k6 = K(6);
k_1 = K(7);
k_2 = K(8);
k_3 = K(9);
k_4 = K(10);
k_5 = K(11);
k_6 = K(12);
 
%%
%  numerator
E(1) = k6*k_1*k_3*k5*C+k6*k_1*k_3*k_2+k6*k_1*k_3*k_4+k6*k_1*k5*C*k4*A+k6*k_1*k_2*k4*A+k6*k_3*k5*C*k2*B+k6*k_3*k_4*k2*B+k6*k5*C*k2*B*k4*A+k_1*k_3*k_2*k_5+k_1*k_3*k_4*k_5+k_1*k_2*k_5*k4*A+k_3*k_4*k_5*k2*B; 
E(2) = k_6*P*k5*C*k_1*k_3+k_6*P*k_1*k_3*k_2+k_6*P*k_1*k_3*k_4+k_6*P*k5*C*k_1*k4*A+k_6*P*k_1*k_2*k4*A+k_6*P*k5*C*k_3*k2*B+k_6*P*k_3*k_4*k2*B+k_6*P*k5*C*k2*B*k4*A+k5*C*k2*B*k1*A*k_3+k5*C*k4*A*k3*B*k_1+k5*C*k2*B*k4*A*k1*A+k5*C*k2*B*k4*A*k3*B; 
E(3) = k1*A*k6*k_3*k5*C+k1*A*k_2*k6*k_3+k1*A*k6*k_3*k_4+k1*A*k6*k5*C*k4*A+k1*A*k_2*k6*k4*A+k_2*k_5*k_6*P*k_3+k_2*k4*A*k3*B*k6+k_2*k_5*k4*A*k_6*P+k1*A*k_2*k_3*k_5+k1*A*k_3*k_4*k_5+k1*A*k_2*k_5*k4*A+k_2*k_5*k4*A*k3*B; 
E(4) = k_5*k_6*P*k_1*k_3+k2*B*k1*A*k6*k_3+k4*A*k3*B*k6*k_1+k_5*k4*A*k_6*P*k_1+k2*B*k4*A*k1*A*k6+k_5*k2*B*k_6*P*k_3+k2*B*k4*A*k3*B*k6+k_5*k2*B*k4*A*k_6*P+k_5*k2*B*k1*A*k_3+k_5*k4*A*k3*B*k_1+k_5*k2*B*k4*A*k1*A+k_5*k2*B*k4*A*k3*B; 
E(5) = k3*B*k6*k_1*k5*C+k3*B*k6*k_1*k_2+k3*B*k_4*k6*k_1+k_4*k_5*k_6*P*k_1+k_4*k2*B*k1*A*k6+k3*B*k6*k5*C*k2*B+k3*B*k_4*k6*k2*B+k_4*k_5*k2*B*k_6*P+k3*B*k_1*k_2*k_5+k3*B*k_4*k_1*k_5+k_4*k_5*k2*B*k1*A+k3*B*k_4*k_5*k2*B; 
 
%%
% denominator 
D = E(1) + E(2) + E(3) + E(4) + E(5); 
%%
% fractions 
F(1) = E(1)/D;
F(2) = E(2)/D;
F(3) = E(3)/D;
F(4) = E(4)/D;
F(5) = E(5)/D;