* NLP literature problem
* Shekel function, Dixon and Szego (1975)

VARIABLES
	 x  
	 y  
     objval    objective function variable;

FREE VARIABLES    objval;


EQUATIONS
	 f Objective function;

f  .. objval =e=(-1)/(POWER(x-4,2)+POWER(y-4,2)+0.1)-(1/(POWER(x-1,2)+POWER(y-1,2)+0.2))-(1/(POWER(x-8,2)+POWER(y-8,2)+0.2));

* Starting point (global solution)
* x.L = 4;
* y.L = 4;

MODEL test /ALL/;
SOLVE test USING NLP MINIMIZING objval;