function ASAE = modelerror(A, B) % evaluates the Average Sum of Absolute Error of the passed model
%
% Author: Wesam ELSHAMY
% wesamelshamy@ieee.org
% Electrical Engineering Dept., Cairo University, Egypt

global Na Nb Nk Y U

A = A(2 : end);             % removing the leading 1
B = B(Nk + 1 : end);        % removing the leading zeros
e = zeros(1, size(Y, 1));
a = zeros(1, size(A, 2));
b = zeros(1, size(B, 2));

for x = 1 : size(A, 2)
    a(x) = A(size(A, 2) - x + 1);
end
for x = 1 : size(B, 2)
    b(x) = B(size(B, 2) - x + 1);
end

for t = max(Na + 1, Nb + Nk) : size(Y, 1)
    e(t) = Y(t) + a*Y(t - Na : t - 1) - b*U(t - Nk - Nb + 1 : t - Nk); % ARX model
end

ASAE = sum(abs(e))/size(e, 2);  % and calculates the fitness