Originally posted by: Laser.Cho

Hi. I'm using latest Cplex studio in windows 7.

I tried a really simple code below for test. I expected 2 optimized solutions.(it has 2 solution) 

===============

dvar float x;

dexpr float res=(x+2)*(x-2)*(x+4)*(x-4);

minimize 
    res;

===============

The result is error.

The only message I got is "CPLEX(default) cannot extract expression: (((x+2)*(x+(-2)))*(x+4))*(x+(-4)).

I cannot understand why it happened. Quadratic equation is not surported? 

Hi,

when you deal with such non linear nor quadratic objective you could try Constraint Programming:

using CP;
 
 int scale=1000000;
 
 dvar int scalex in -100*scale..100*scale;
 
 
 dexpr float x=scalex/scale;

dexpr float res=(x+2)*(x-2)*(x+4)*(x-4);

minimize
    res;
    
subject to
{

}    
    
    
execute
{
writeln(x);
}   

gives

-3.167115

regards

Originally posted by: Laser.Cho

I really appreciate you to answer my Question. thanx.

now i know I have to learn CP programming. 

Can you tell me why what I did is wrong? and is there way to show other optimal solutions if exist? 

Hi,

even without CP you could have written

dvar float x2; //x2=x*x
dexpr float res=(x2-4)*(x2-16);

minimize
        res;
        
    subject to
    {

    }    
        
        
execute
    {
    writeln(Opl.sqrt(x2));
    }  

and then you get

3.16227766

regards