CEC 2010 F1 gives negative value

[Md-Ashraful-Pramanik]

CEC 2010 F1 gives negative objective value. In code I found -abs(...) in the implementation of the function.

function PopObj = CalObj(obj,PopDec)
    Z = PopDec - repmat(obj.O(1:size(PopDec,2)),size(PopDec,1),1);
    PopObj = -abs(sum((cos(Z).^4),2)-2*prod((cos(Z).^2),2))./sqrt(sum(repmat(1:size(Z,2),size(Z,1),1).*(Z.^2),2));
end