[GAP Forum] Square root of cyclotomic real number

[Marek Mitros]

Dear All,

I am doing following calculation and I need square root of cyclotomic
number being real number. Here is example below. Is there any workaround
for this ?
What I am doing I obtained vector v of complex number which not unit
length. In order to normalize it I perform following and I receive the
error. Do I need more knowledge about cyclotomic numbers ?

gap> v1:=v/Sqrt(v*ComplexConjugate(v));

Error, no method found! For debugging hints type ?Recovery from
NoMethodFound

Error, no 1st choice method found for `Sqrt' on 1 arguments called from

<function "HANDLE_METHOD_NOT_FOUND">( <arguments> )

(...)

gap> n:=E(20)-E(20)^9;

E(20)-E(20)^9

gap> RealPart(n);

E(20)-E(20)^9

gap> Sqrt(n);

Error, no method found! For debugging hints type ?Recovery from
NoMethodFound

Error, no 1st choice method found for `Sqrt' on 1 arguments called from


Regards,

Marek