)abbrev package NORMRETR NormRetractPackage
++ Description:
++ This package \undocumented
NormRetractPackage(F, ExtF, SUEx, ExtP, n) : C  == T where
  F          :   FiniteFieldCategory
  ExtF       :   FiniteAlgebraicExtensionField(F)
  SUEx       :   UnivariatePolynomialCategory ExtF
  ExtP       :   UnivariatePolynomialCategory SUEx
  n          :   PositiveInteger
  SUP       ==>  SparseUnivariatePolynomial
  R         ==>  SUP F
  P         ==>  SUP R

  C  ==> with
      normFactors : ExtP -> List ExtP
        ++ normFactors(x) \undocumented
      retractIfCan : ExtP -> Union(P, "failed")
        ++ retractIfCan(x) \undocumented
      Frobenius    : ExtP -> ExtP
        ++ Frobenius(x) \undocumented

  T  ==> add

      normFactors(p : ExtP) : List ExtP ==
          facs : List ExtP := [p]
          for i in 1..n-1 repeat
             member?((p := Frobenius p), facs) => return facs
             facs := cons(p, facs)
          facs

      Frobenius(ff : ExtP) : ExtP ==
         fft : ExtP := 0
         while ff ~= 0 repeat
           fft := fft + monomial(map(Frobenius, leadingCoefficient ff),
                               degree ff)
           ff := reductum ff
         fft

      retractIfCan(ff:ExtP):Union(P, "failed") ==
         fft : P := 0
         while ff ~= 0 repeat
           lc : SUEx := leadingCoefficient ff
           plc : SUP F := 0
           while lc ~= 0 repeat
              lclc : ExtF := leadingCoefficient lc
              (retlc := retractIfCan lclc) case "failed" => return "failed"
              plc := plc + monomial(retlc@F, degree lc)
              lc := reductum lc
           fft := fft+monomial(plc, degree ff)
           ff := reductum ff
         fft

)abbrev package TWOFACT TwoFactorize
++ Authors : P.Gianni, J.H.Davenport
++ Date Created : May 1990
++ Description:
++ A basic package for the factorization of bivariate polynomials
++ over a finite field.
++ The functions here represent the base step for the multivariate factorizer.

TwoFactorize(F) : C == T
 where
  F          :   FiniteFieldCategory
  SUP       ==>  SparseUnivariatePolynomial
  R         ==>  SUP F
  P         ==>  SUP R
  UPCF2     ==>  UnivariatePolynomialCategoryFunctions2

  C == with
    generalTwoFactor    : (P)  ->  Factored P
      ++ generalTwoFactor(p) returns the factorisation of polynomial p,
      ++ a sparse univariate polynomial (sup) over a
      ++ sup over F.
    tryTwoFactor   : (P) -> Factored P
      ++ tryTwoFactor(p) returns the factorisation of polynomial p,
      ++ if it does not require using field extensions, otherwise
      ++ returns p unfactored (nil factorization).
    doFactor : (P, Integer, Boolean) -> Factored P
      ++ doFactor(p, n, ext?) returns the factorisation of polynomial p,
      ++ p is assumed to be primitive and squarefree,
      ++ n is degree in auxilary variable, ext? if false inhibits
      ++ use of extension field.

  T == add
    PI ==> PositiveInteger
    NNI ==> NonNegativeInteger
    import from CommuteUnivariatePolynomialCategory(F, R, P)

                   ----  Local Functions  ----
    pthRoot        :     (R, NNI, NNI)    -> R


    pthRoot(poly : R, p : NonNegativeInteger, PthRootPow : NonNegativeInteger) : R ==
       tmp := divideExponents(map((x : F) : F +-> (x::F)^PthRootPow, poly), p)
       tmp case "failed" => error "consistency error in TwoFactor"
       tmp

    fUnion ==> Union("nil", "sqfr", "irred", "prime")
    FF     ==> Record(flag : fUnion, factor : P, exponent : NNI)

    doTwoFactor : (P, Boolean) -> Factored P

    tryTwoFactor(m : P) : Factored P ==
       doTwoFactor(m, false)

    generalTwoFactor(m : P) : Factored P ==
       doTwoFactor(m, true)

    doTwoFactor(m : P, do_ext : Boolean) : Factored P ==
       m = 0 => 0
       degree m = 0 =>
         l := factor(leadingCoefficient(m)
                    )$UnivariateFiniteFieldFactorize(F, R)
         makeFR(unit(l)::P, [[u.flag, u.factor::P, u.exponent] for u in factorList l])
       ll : List FF
       ll := []
       unitPart : P
       cont := content m
       if degree(cont)>0 then
          m1 := m exquo cont
          m1 case "failed" => error "content doesn't divide"
          m := m1
          contfact := factor(cont)$UnivariateFiniteFieldFactorize(F, R)
          unitPart := (unit contfact)::P
          ll := [[w.flag, (w.factor)::P, w.exponent] for w in factorList contfact]
       else
          unitPart := cont::P
       sqfrm := squareFree m
       for u in factorList sqfrm repeat
           expon := u.exponent
           fac := u.factor
           degree fac = 1 => ll := [["prime", fac,expon], :ll]
           differentiate fac = 0 =>
              -- the polynomial is  inseparable w.r.t. its main variable
              map(differentiate, fac) = 0 =>
                p := characteristic$F
                PthRootPow := (size$F exquo p)::NonNegativeInteger
                m1 := divideExponents(
                       map(x +-> pthRoot(x, p, PthRootPow), fac), p)
                m1 case "failed" => error "consistency error in TwoFactor"
                res := generalTwoFactor m1
                unitPart := unitPart*unit(res)^((p*expon)::NNI)
                ll := [:[[v.flag, v.factor, expon *p*v.exponent] for v in factorList res], :ll]
              m2 := generalTwoFactor swap fac
              unitPart := unitPart*unit(m2)^(expon::NNI)
              ll := [:[[v.flag, swap v.factor, expon*v.exponent] for v in factorList m2], :ll]
           ydeg := "max"/[degree w for w in coefficients fac]
           twoF := doFactor(fac, ydeg, do_ext)
           nfl := factorList(twoF)
           #nfl = 1 and nfl(1).flag case "nil" =>
               return twoF
           unitPart := unitPart*unit(twoF)^expon
           ll := [:[[v.flag, v.factor, expon*v.exponent] for v in factorList twoF],
                 :ll]
       makeFR(unitPart, ll)


    doExtension1(m : P, n : PI, dx : Integer,
      extField : FiniteAlgebraicExtensionField(F)) : Factored P ==
        SUEx := SUP extField
        TP := SparseUnivariatePolynomial SUEx
        mm : TP := 0
        m1 := m
        while m1 ~= 0 repeat
            mm := mm + monomial(map(coerce, leadingCoefficient m1)$UPCF2(
                         F, R, extField, SUEx), degree m1)
            m1 := reductum m1
        res1 := doFactor(mm, dx, false)$TwoFactorize(extField)
        flist := factorList res1
        #flist = 1 =>
            first(flist).flag = "prime" => primeFactor(m, 1)
            nilFactor(m, 1)
        Normp := NormRetractPackage(F, extField, SUEx, TP, n)
        lfacth := [fac.factor for fac in flist]
        lfactk : List P := []
        while not empty? lfacth repeat
            ff := first lfacth
            lfacth := rest lfacth
            if (c := leadingCoefficient leadingCoefficient ff) ~= 1 then
                ff := ((inv c)::SUEx)*ff
            not ((ffu := retractIfCan(ff)$Normp) case "failed") =>
                    lfactk := cons(ffu@P, lfactk)
            normfacs := normFactors(ff)$Normp
            lfacth := [g for g in lfacth | not member?(g, normfacs)]
            ffn := */normfacs
            lfactk := cons(retractIfCan(ffn)$Normp::P, lfactk)
        */[primeFactor(ff1, 1) for ff1 in lfactk]

    doExtension(m : P, dx : Integer) : Factored P ==
        ln : List(PI) := [2, 3, 5, 7, 9, 11, 13, 17, 19, 23, 29]
        for n in ln repeat
            nsize := size()$F ^ n
            res1 :=
                nsize < 1000 => doExtension1(m, n, dx,
                      FiniteFieldCyclicGroupExtension(F, n))
                doExtension1(m, n, dx, FiniteFieldExtension(F, n))
            first(factorList(res1)).flag = "prime" => return res1
        error "doExtension : Impossible"

    doFactor(m : P, dx : Integer, do_ext : Boolean) : Factored P ==
        look : Boolean := true
        try_max : Integer := min(dx + 5, size()$F)
        i : Integer := 0
        lcm := leadingCoefficient m
        umv : R
        val : F
        use_random := 2*try_max < size()$F
        while look and i < try_max repeat
            i := i + 1
            if use_random then
                val := random()$F
            else
                val := index(qcoerce(i)@PositiveInteger)$F
            zero? elt(lcm, val) => "next value"
            umv := map(x +-> elt(x, val), m)$UPCF2(R, P, F, R)
            degree(gcd(umv, differentiate umv)) ~= 0 => "next val"
            look := false
        look and not do_ext => return nilFactor(m, 1)
        look => doExtension(m, dx)

        prime : R := monomial(1, 1) - monomial(val, 0)
        fumv := factor(umv)$UnivariateFiniteFieldFactorize(F, R)
        lfact1 := factorList fumv

        #lfact1 = 1 => primeFactor(m, 1)
        lfact : List P := [map(coerce, lf.factor)$UPCF2(F, R, R, P)
                             for lf in lfact1]
        lfact := cons(map(coerce, unit fumv)$UPCF2(F, R, R, P),
                      lfact)
        import from GeneralHenselPackage(R, P)
        dx1 : PI := (dx + 1)::PI
        lfacth := completeHensel(m, lfact, prime, dx1)
        lfactk : List P := []
        while not empty? lfacth repeat
            ff := first lfacth
            lfacth := rest lfacth
            if (c := leadingCoefficient leadingCoefficient ff) ~= 1 then
                ff := ((inv c)::R)* ff
            lfactk := cons(ff, lfactk)
        */[primeFactor(ff1, 1) for ff1 in lfactk]

--Copyright (c) 1991-2002, The Numerical ALgorithms Group Ltd.
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