function S=test(x)
% Cragg & Levy, 1969
% x0 = [1, 2, 2, 2]'
% xo = [0, 1, 1, 1+/-n*PI]'
% S(xo) = 0

S=(exp(x(1))-x(2)).^4+100*(x(2)-x(3)).^6+(tan(x(3)-x(4))).^4+x(1).^8+(x(4)-1).^2;
