Set j /0*1/;

Scalar PI / 3.14159265359 / ;

Variable x(j), z;

x.lo['0'] = -10 ;
x.up['0'] =  10 ;
x.lo['1'] = -10 ;
x.up['1'] =  10 ;

$macro defobj 0.25*power(x['0'],4)-0.5*x['0']*x['0']+0.1*x['0']+0.5*x['1']*x['1']

Equation
         Def_obj;
Def_obj..

z =e= defobj ;

model m /all/;

solve m min z using nlp;

$onDotL  
file fx / AluffiPentini.txt /; fx.nd=12; fx.nw=22; put fx;
scalar cnt; for (cnt=1 to 100,
x.l(j) = uniform(x.lo(j), x.up(j));
z.l = defobj  ;

loop(j, put x.l(j)); put z.l /);