GaloisGroup_Sequence.mag

declare type PGGAlg_GaloisGroup_Sequence: PGGAlg_GaloisGroup;
declare attributes PGGAlg_GaloisGroup_Sequence: algs;

intrinsic PGGAlg_GaloisGroup_Sequence_Make(algs) -> PGGAlg_GaloisGroup_Sequence
  {The algorithm which tries each algorithm in algs in turn.}
  alg := New(PGGAlg_GaloisGroup_Sequence);
  alg`algs := algs;
  return alg;
end intrinsic;

intrinsic Print(alg :: PGGAlg_GaloisGroup_Sequence)
  {Print.}
  printf "sequence";
  if #alg`algs eq 0 then
    printf " (empty)";
  else
    for i in [1..#alg`algs] do
      print "";
      IndentPush();
      printf "%o: ", i;
      Print(alg`algs[i]);
      IndentPop();
    end for;
  end if;
end intrinsic;

intrinsic TryGaloisGroup(alg :: PGGAlg_GaloisGroup_Sequence, f :: PGGPol) -> BoolElt, .
  {The Galois group of f.}
  errs := [Strings()| ];
  for a in alg`algs do
    vprint PGG_GaloisGroup: "trying algorithm:", a;
    ok, G := TryGaloisGroup(a, f);
    if ok then
      return true, G;
    else
      Append(~errs, G);
      vprint PGG_GaloisGroup: "failed:", G;
    end if;
  end for;
  if #errs eq 0 then
    return false, "nothing to try";
  elif #errs eq 1 then
    return false, errs[1];
  else
    return false, "no algorithm succeeded (" cat Join(errs, "; ") cat ")";
  end if;
end intrinsic;