function f=cstrF(x)
% Reactor in series model, the function.
%
% x = [C(1),C(2),... C(N-1),beta]
% f(i) = beta C(i)^2 + C(i) - C(i-1)

global N CN

N = length(x); % Number of unknowns and number of reactors.
C0 = 5.0;      % Inlet concentration (mol/L).
CN = 0.5;      % Outlet concentration (mol/L).

% Initialize array (column vector format).
f = zeros(N,1);

f(1) = x(N)*x(1)^2.0+x(1)-C0;
for i=2:N-1
 f(i)= x(N)*x(i)^2.0+x(i)-x(i-1);
end
f(N) = x(N)*CN^2.0+CN-x(N-1);