param N := 3;

var x{1..N};
var u;
param pi := 3.1415;

minimize f:
100*((x[3]-10*u)^2 + ((x[1]^2+x[2]^2)^0.5-1)^2)+x[3]^2;

subject to cons1:
u = if (x[1]>0) then (1/(2*pi))*atan(x[2]/x[1]) else 0.5 + (1/(2*pi))*atan(x[2]/x[1]);

subject to cons2:
0.1 <= x[1];

subject to cons3:
-2.5 <= x[3] <= 7.5;

data;
var x:=
1	-1
2	0
3	0;

solve;

display x;