[GAP Forum] real value approximation

[Paraskevas Alvanos]

Dear GAP forum,

I would like to know if there is a way to have evaluate the primitive  
element of a numberfield

i.e.

x := Indeterminate(Rationals);
g := x ^2 - 2;
F := FieldByPolynomial(g);
a := PrimitiveElement(F);

Is it a way to determine which conjugate a. Can I have an approximate  
real value of a;
Of course a can simple ask

a>0;

and wait for true or false,
but when I have 10-20 real and complex conjugates should I find a  
constructive way to understand which is my primitive element or there  
is something much easier that I am missing.

Thanks everybody in advance
paraskevas alvanos