* Generalized geometric programming problem
* Robust stability analysis
* Gaston and Safonov (1988)


VARIABLES
	 q1  
	 q2  
	 q3  
	 k   margin of stability
     objval    objective function variable;

FREE VARIABLES    objval;
POSITIVE VARIABLES q1, q2, q3, k; 


EQUATIONS
	 f Objective function
	 g  
	 b1l  
	 b1u
	 b2l 
	 b2u
	 b3l
	 b3u;

f  .. objval =e=k;
g  .. 10*POWER(q2,2)*POWER(q3,3) + 10*POWER(q2,3)*POWER(q3,2) + 200*POWER(q2,2)*POWER(q3,2) + 100*POWER(q2,3)*q3 + 100*q2*POWER(q3,3) + q1*q2*POWER(q3,2) + q1*POWER(q2,2)*q3 + 1000*q2*POWER(q3,2) + 8*q1*POWER(q3,2) + 1000*POWER(q2,2)*q3 + 8*q1*POWER(q2,2) + 6*q1*q2*q3 - POWER(q1,2) + 60*q1*q3 + 60*q1*q2 -200*q1 =l= 0;
b1l  .. -800*k - q1 =l= -800;
b1u  .. -800*k + q1 =l= 800;
b2l  .. -2*k - q2 =l= -4;
b2u  .. -2*k + q2 =l= 4;
b3l  .. -3*k - q3 =l= -6;
b3u  .. -3*k + q3 =l= 6;

* Starting point (global solution)
* k.L = 0.3417;
* q1.L = 1073.4;
* q2.L = 3.318;
* q3.L = 4.975;


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