galoischartable

Function: galoischartable
Section: number_fields
C-Name: galoischartable
Prototype: G
Help: galoischartable(gal): return the character table of the underlying
 group of gal.
Doc: Compute the character table of~$G$, where~$G$ is the underlying group of
 the \kbd{galoisinit} structure~\var{gal}. The input~\var{gal} is also allowed
 to be a \typ{VEC} of permutations that is closed under products.
 Let~$N$ be the number of conjugacy classes of~$G$.
 Return a \typ{VEC}~$[M,\var{e}]$ where $e \geq 1$ is an integer
 and $M$ is a square \typ{MAT} of size~$N$ giving the character table
 of~$G$.

 \item Each column corresponds to an irreducible character; the characters
 are ordered by increasing dimension and the first column is the trivial
 character (hence contains only $1$'s).

 \item Each row corresponds to a conjugacy class; the conjugacy classes are
 ordered as specified by \kbd{galoisconjclasses(gal)}, in particular the
 first row corresponds to the identity and gives the dimension $\chi(1)$
 of the irreducible representation attached to the successive characters
 $\chi$.

 The value $M[i,j]$ of the character $j$ at the conjugacy class $i$
 is represented by a polynomial in \kbd{y} whose variable should be
 interpreted as an $e$-th root of unity, i.e. as the lift of
 \bprog
   Mod(y, polcyclo(e,'y))
 @eprog\noindent (Note that $M$ is the transpose of the usual orientation for
 character tables.)

 The integer $e$ divides the exponent of the group $G$ and is chosen as small
 as posible; for instance $e = 1$ when the characters are all defined over
 $\Q$, as is the case for $S_n$. Examples:
 \bprog
 ? K = nfsplitting(x^4+x+1);
 ? gal = galoisinit(K);
 ? [M,e] = galoischartable(gal);
 ? M~  \\ take the transpose to get the usual orientation
 %4 =
 [1  1  1  1  1]

 [1 -1 -1  1  1]

 [2  0  0 -1  2]

 [3 -1  1  0 -1]

 [3  1 -1  0 -1]
 ? e
 %5 = 1
 ? {G = [Vecsmall([1, 2, 3, 4, 5]), Vecsmall([1, 5, 4, 3, 2]),
         Vecsmall([2, 1, 5, 4, 3]), Vecsmall([2, 3, 4, 5, 1]),
         Vecsmall([3, 2, 1, 5, 4]), Vecsmall([3, 4, 5, 1, 2]),
         Vecsmall([4, 3, 2, 1, 5]), Vecsmall([4, 5, 1, 2, 3]),
         Vecsmall([5, 1, 2, 3, 4]), Vecsmall([5, 4, 3, 2, 1])];}
   \\G = D10
 ? [M,e] = galoischartable(G);
 ? M~
 %8 =
 [1  1              1              1]

 [1 -1              1              1]

 [2  0 -y^3 - y^2 - 1      y^3 + y^2]

 [2  0      y^3 + y^2 -y^3 - y^2 - 1]
 ? e
 %9 = 5
 @eprog