I. Duality. Macaulay F. S., The Algebraic Theory of Modular Systems, Cambridge Univ. Press (1916);

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1 I. Duality Macaulay F. S., On the Resolution of a given Modular System into Primary Systems including some Properties of Hilbert Numbers, Math. Ann. 74 (1913), ; Macaulay F. S., The Algebraic Theory of Modular Systems, Cambridge Univ. Press (1916); Gröbner W., Moderne Algebraische Geometrie, Springer (1949); Möller H.M., Systems of Algebraic Equations Solved by Means of Endomorphisms, L. N. Comp. Sci. 673 (1993), 43 56, Springer; Marinari M.G., Möller H.M., On multiplicities in Polynomial System Solvin. Trans. AMS, 348 (1996), ; Alonso M.E., Marinari M.G., The big Mother of all Dualities 2: Macaulay Bases, J AAECC To appear 1

2 P := k[x 1,..., X n ], L := {l 1,..., l r } P be a linearly indipendent set of k-linear functionals such that L := Span k (L) is a P-module so that I := P(L) is a zero-dimensional ideal; N(I) := {t 1,..., t r }, q := {q 1,..., q r } P the set triangular to L, obtained via Möller s Algorithm; ( q (h) ij ) k r2, 1 k r be the matrices defined by X h q i = j q (h) ij q j mod I, Λ := {λ 1,..., λ r } be the set biorthogonal to q, which can be trivially deduced by Gaussian reduction Then X h λ j = r i=1 q (h) ij λ i, i, j, h. 2

3 P := k[x 1,..., X n ]; T := {X a 1 1 Xa n n : (a 1,..., a n ) N n }; m := (X 1,..., X n ) be the maximal at the origin; I P an ideal; the m-closuse of I is the ideal d I + m d ; I is m-closed iff I = d I + m d ; For each τ T, denote M(τ) : P k the morphism defined by M(τ) = c(f, τ), f = t T c(f, t)t P. Denoting M := {M(τ) : τ T } for all f := t T a t t P and l := it holds l(f) = t T a t c t. τ T c τ M(τ) k[[m]] = P τ T, X i M(τ) = M( τ X i ) if X i τ 0 if X i τ A k-vector subspace Λ Span k (M) is called stable if λ Λ = X i λ Λ i.e. Λ is a P-module. 3

4 Clealy P = k[[m]]; however in order to have reasonable duality we must restrict ourselves to Span k (M) = k[m]. For each k-vector subspace Λ Span k (M) denote I(Λ) := P(Λ) = {f P : l(f) = 0, l Λ} and for each k-vector subspace P P denote M(P ) := L(P ) Span K (M) = {l Span K (M) : l(f) = 0, f P }. The mutually inverse maps I( ) and M( ) give a biunivocal, inclusion reversing, correspondence between the set of the m-closed ideals I P and the set of the stable k-vector subspaces Λ Span k (M). They are the restriction of, respectively, P( ) to m-closed ideals I P, and L( ) to stable k-vector subspaces Λ Span k (M). Moreover, for any m-primary ideal q P, M(q) is finite k-dimensional and we have deg(q) = dim K (M(q)); conversely for any finite k-dim. stable k-vector subspace Λ Span K (M), I(Λ) is an m-primary ideal and we have dim k (Λ) = deg(i(λ)). 4

5 II. Macaulay Bases Macaulay F. S., On the Resolution of a given Modular System into Primary Systems including some Properties of Hilbert Numbers, Math. Ann. 74 (1913), ; Macaulay F. S., The Algebraic Theory of Modular Systems, Cambridge Univ. Press (1916); Gröbner W., Moderne Algebraische Geometrie, Springer (1949); Möller H.M., Systems of Algebraic Equations Solved by Means of Endomorphisms, L. N. Comp. Sci. 673 (1993), 43 56, Springer; Marinari M.G., Möller H.M., On multiplicities in Polynomial System Solvin. Trans. AMS, 348 (1996), ; Alonso M.E., Marinari M.G., The big Mother of all Dualities 2: Macaulay Bases, J AAECC To appear 5

6 Let < be a semigroup ordering on T and I P an m-closed ideal. Can(t, I, <) =: τ N < (I) so that t τ N < (I) γ(t, τ, <)τ I, t < τ = γ(t, τ, <) = 0. γ(t, τ, <)τ k[[n < (I)]] k[[x 1,..., X n ]] Define, for each τ N < (I), l(τ) := M(τ) + t T < (I) γ(t, τ, <)M(t) k[[m]]. Remark that l(τ) M(I) requires l(τ) k[m] which holds iff {t : γ(t, τ, <) 0} is finite and is granted if {t : t > τ} is finite. To obtain this we must choose as < a standard ordering i.e. such that X i < 1, i, for each infinite decreasing sequence in T τ 1 > τ 2 > τ ν > and each τ T there is ν : τ > τ n. In this setting the generalization of the notion of Gröbner basis is called Hironoka/standard basis and deals with series instead of polynomials. The choice of this setting is natural, since a Hironaka basis of an ideal I returns its m-closure. 6

7 Let < be a standard ordering on T and let I P an m-closed ideal. Denote Can(t, I, <) =: τ N < (I) and, for each τ N < (I), l(τ) := M(τ) + t T < (I) γ(t, τ, <)τ k[[n < (I)]] γ(t, τ, <)M(t) k[m]. Then M(I) = Span k {l(τ), τ N < (I)}. The set {l(τ), τ N < (I)} is called the Macaulay Basis of I. There is an algorithm which, given a finite basis (not necessarily Gröbner/standard) of an m- primary ideal I, computes its Macaulay Basis. Such algorithm becomes an infinite procedure which, given a finite basis of an ideal I m, returns the infinite Macaulay Basis of its m-closure. 7

8 III. Cerlienco Mureddu Correspondence Cerlienco, L, Mureddu, M. Algoritmi combinatori per l interpolazione polinomiale in dimensione 2. Preprint (1990) Cerlienco L., Mureddu M., From algebraic sets to monomial linear bases by means of combinatorial algorithms Discrete Math., 139 (1995), Cerlienco L., Mureddu M., Multivariate Interpolation and Standard Bases for Macaulay Modules, J. Algebra 251 (2002), Problem 1 Given a finite set of points, {a 1,..., a s } k n, a i := (a i1,..., a in ), to compute N < (I) w.r.t. the lexicographical ordering < induced by X 1 < < X n where I := {f P : f(a i ) = 0, 1 i s}. 8

9 Cerlienco Mureddu Algorithm, to each ordered finite set of points X := {a 1,..., a s } k n, a i := (a i1,..., a in ), associates an order ideal N := N(X) and a bijection Φ := Φ(X) : X N which satisfies Theorem 1 N(I) = N(X) holds for each finite set of points X k n. Since they do so by induction on s = #(X) let us consider the subset X := {a 1,..., a s 1 }, and the corresponding order ideal N := N(X ) and bijection Φ := Φ(X ). If s = 1 the only possible solution is N = {1}, Φ(a 1 ) = 1. 9

10 T [1, m] := T k[x 1,..., X m ] = {X a 1 1 Xa m m : (a 1,..., a m ) N m }, π m : k n k m, π m (x 1,..., x n ) = (x 1,..., x m ), π m : T = N n N m = T [1, m], π m (X a 1 1 Xa n n ) = X a 1 1 Xa m m. With this notation, let us set m := max ( j : i < s : π j (a i ) = π j (a s ) ) ; d := #{a i, i < s : π m (a i ) = π m (a s )}; W := {a i : Φ (a i ) = τ i X d m+1, τ i T [1, m]} {a s }; Z := π m (W); τ := Φ(Z)(π m (a s )); t s := τx d m+1 ; where N(Z) and Φ(Z) are the result of the application of the present algorithm to Z, which can be inductively applied since #(Z) s 1. We then define N := N {t s }, Φ(a i ) := Φ (a i ) t s i < s i = s 10

11 a 1 := (0, 0, 1), Φ(a 1 ) := t 1 := 1; a 2 := (0, 1, 2), m = 1, d = 1, W = {(0, 1)}, τ = 1, Φ(a 2 ) := t 2 := X 2, a 3 := (2, 0, 2), m = 0, d = 1, W = {(2, 0)}, τ = 1, Φ(a 3 ) := t 3 := X 1, a 4 := (0, 2, 2), m = 1, d = 2, W = {(0, 2)}, τ = 1, Φ(a 4 ) := t 4 := X 2 2, a 5 := (1, 0, 3), m = 0, d = 2, W = {(1, 0)}, τ = 1, Φ(a 5 ) := t 5 := X 2 1, a 6 := (1, 1, 3), m = 1, d = 1, W = {(0, 1), (1, 1)}, τ = X 1, Φ(a 6 ) := t 6 := X 1 X 2. (0, 2, 2) (0, 1, 2) (1, 1, 3) (0, 0, 1) (2, 0, 2) (1, 0, 3) 11

12 a 7 := (1, 1, 1), m = 2, d = 1, W = {(1, 1, 1)}, τ = 1, Φ(a 7 ) := t 7 := X 3. a 8 := (2, 0, 1), m = 2, d = 1, W = {(1, 1, 1), (2, 0, 1)}, τ = X 1, Φ(a 8 ) := t 8 := X 1 X 3, a 9 := (2, 0, 0), m = 2, d = 2, W = {(2, 0, 0))}, τ = 1, Φ(a 9 ) := t 9 := X 2 3, (0, 2, 2) (0, 1, 2) (1, 1, 3) (0, 0, 1) (2, 0, 2) (1, 0, 3) 12

13 Gao S., Rodrigues V.M., Stroomer J., Gröbner basis structure of finite sets of points Preprint (2003) A combinatorial reformulation which builds a tree on the basis of the point coordinates, cominatorially recombines the tree, reeds on this tree the monomial structure. It returns N but not Φ; more important: it is not iterative. Marinari M.G., Cerlienco Mureddu Correpondence and Lazard Structural Theorem. Investigaciones Mathematicas (2006). To appear. Extends Cerlienco Mureddu Algorithm to multiple points described via Macaulay Bases 13

14 IV. Macaulay s Algorithm Macaulay F. S., On the Resolution of a given Modular System into Primary Systems including some Properties of Hilbert Numbers, Math. Ann. 74 (1913), ; Macaulay F. S., The Algebraic Theory of Modular Systems, Cambridge Univ. Press (1916); Gröbner W., Moderne Algebraische Geometrie, Springer (1949); Alonso M.E., Marinari M.G., The big Mother of all Dualities 2: Macaulay Bases, J AAECC To appear 14

15 m = (X 1,..., X n ) P := k[x 1,..., X n ], T := {X a 1 1 Xa n n : (a 1,..., a n ) N n }, a standard-ordering < on T, an m-closed ideal I, the finite corner set C < (I) := {ω 1,..., ω s }, the (not-necessarily finite) set N < (I), the Macaulay basis {l(τ) : τ N < (I)}, the k-vectorspace Λ Span k (M) generated by it

16 q q j = M(q ) Λ j. 16 m = (X 1,..., X n ) P := k[x 1,..., X n ], T := {X a 1 1 Xa n n : (a 1,..., a n ) N n }, a standard-ordering < on T, an m-closed ideal I, the finite corner set C < (I) := {ω 1,..., ω s }, the (not-necessarily finite) set N < (I), the Macaulay basis {l(τ) : τ N < (I)}, Λ := Span k {l(τ) : τ N < (I)} Span k (M); j, 1 j s, Λ j := Span k {υ l(ω j ) : υ T }. j, 1 j s, q j := I(Λ j ). Let J {1,..., s} be the set such that {q j : j J} is the set of the minimal elements of {q j : 1 j s} and remark that q i q j Λ i Λ j. Lemma 1 (Macaulay) With the notation above, for each j, denoting we have Λ j := Span K{υ l(ω j ) : υ T m} dim K (Λ j ) = dim K(Λ j ) 1, l(ω j ) / Λ j = M(q j : m),

17 m = (X 1,..., X n ) P := k[x 1,..., X n ], T := {X a 1 1 Xa n n : (a 1,..., a n ) N n }, a standard-ordering < on T, an m-closed ideal I, the finite corner set C < (I) := {ω 1,..., ω s }, the (not-necessarily finite) set N < (I), the Macaulay basis {l(τ) : τ N < (I)}, Λ := Span k {l(τ) : τ N < (I)} Span k (M); j, 1 j s, Λ j := Span k {υ l(ω j ) : υ T }. j, 1 j s, q j := I(Λ j ). Let J {1,..., s} be the set such that {q j : j J} is the set of the minimal elements of {q j : 1 j s} and remark that q i q j Λ i Λ j. Theorem 2 (Gröbner) If I is m-primary, then: 1. each Λ j is a finite-dim. stable vectorspace; 2. each q j is an m-primary ideal, 3. is reduced 4. and irreducible. 5. I := j J q j is a reduced representation of I. 17

18 V. Reduced Irreducible Decomposition Noether Noether E. Idealtheorie in Ringbereichen, Math. Annalen, 83 (1921), Macaulay F. S., On the Resolution of a given Modular System into Primary Systems including some Properties of Hilbert Numbers, Math. Ann. 74 (1913), ; Macaulay F. S., The Algebraic Theory of Modular Systems, Cambridge Univ. Press (1916); Gröbner W., Moderne Algebraische Geometrie, Springer (1949); Renschuch. B, Elementare und praktische Idealtheorie, Deutscher Verlag der Wissenschaften (1976); Alonso M.E., Marinari M.G., The big Mother of all Dualities 2: Macaulay Bases, J AAECC To appear 18

19 (Lasker-Noether) In a noetherian ring R, every ideal a R is a finite intersection of irreducible ideals. (Noether) A representation a = r j=1 i j of an ideal a in a noetherian ring R as intersection of finitely many irreducible ideals is called a reduced representation if j {1,..., r}, i j r and h=1 j h there is no irreducible ideal i j i j such that a = r h=1 j h i h i j. (Noether) In a noetherian ring R, each ideal a = r i=1 i h q i a R has a reduced representation as intersection of finitely many irreducible ideals. A primary component q j of an ideal a contained in a noetherian ring R, is called reduced if there is no primary ideal q j q j such that a = r i=1 j i q i q j. In an irredundant primary decomposition of an ideal of a noetherian ring, each primary component can be chosen to be reduced. 19

20 The decomposition (X 2, XY ) = (X) (X 2, XY, Y λ ), λ N, λ 1, where (X 2, XY, Y λ ) = (X, Y ) (X), shows that embedded components are not unique; however, (X 2, XY, Y ) = (X 2, Y ) (X 2, XY, Y λ ), λ > 1, shows that (X 2, Y ) is a reduced embedded irreducible component and that (X 2, XY ) = (X) (X 2, Y ) is a reduced representation. The decompositions (X 2, XY ) = (X) (X 2, Y + ax), a Q, where (X 2, Y + ax) = (X, Y ) (X) and, clearly, each (X 2, Y + ax) is reduced, show that also reduced representations are not unique; remark that, setting a = 0, we find again the previous one (X 2, XY ) = (X) (X 2, Y ). 20

21 If I is not m-primary, let ρ := max{deg(ω j ) + 1 : ω j C(I)} so that q := I + m ρ is an m-primary component of I; I = r i=1 q i an irredundant primary representation of I with q 1 = m; b := I : m = r i=2 q i; b = u i=1 Q i, a reduced representation of b; q 1 := s j=1 q j a reduced representation of q 1 which is wlog ordered so that q i b i > t; q := t j=1 q j. Then 1. q is a reduced m-primary component of I, 2. q := t j=1 q j is a reduced representation of q, 3. I = u i=1 Q i t j=1 q j is a reduced representation of I. I := (X 2, XY ), Λ = Span k {M(1), M(X)} {M(Y i ), i N}; ρ = 2, M(I + m 2 ) = {M(1), M(X), M(Y )}, ω 1 := X, Λ 1 = {M(1), M(X))}, q 1 = (X 2, Y ), ω 2 := Y, Λ 2 = {M(1), M(Y )}, q 2 = (X, Y 2 ), I : m = (X) (X, Y 2 ), (X 2, XY ) = (X) (X 2, Y ). 21

22 I := (X 2, XY ), Λ = Span k {M(1), M(X)} {M(Y i ), i N}; ρ = 2, M(I + m 2 ) = {M(1), M(X), M(Y )}, ω 1 := X, Λ 1 = {M(1), M(X))}, q 1 = (X 2, Y ), ω 2 := Y, Λ 2 = {M(1), M(Y )}, q 2 = (X, Y 2 ), I : m = (X) (X, Y 2 ), (X 2, XY ) = (X) (X 2, Y ). Both the reduced representation and the notion of Macaulay basis strongly depend on the choice of a frame of coordinates. In fact, considering, for each a Q, a 0, Λ = Span k {M(1), M(X) am(y )} {M(Y i ), i N}, we obtain ρ = 2, M(I + m 2 ) = {M(1), M(X) am(y ), M(Y )}, ω 1 := X, Λ 1 = {M(1), M(X) am(y )}, q 1 = (X 2, Y + ax), ω 2 := Y, Λ 2 = {M(1), M(Y )}, q 2 = (X, Y 2 ), I : m = (X) (X, Y 2 ), (X 2, XY ) = (X) (X 2, Y + ax). 22

23 VI. Lazard Structural Theorem Lazard D., Ideal Basis and Primary Decomposition: Case of two variables J. Symb. Comp. 1 (1985) Theorem 3 Let P := k[x 1, X 2 ] and let < be the lex. ordering induced by X 1 < X 2. Let I P be an ideal and let {f 0, f 1,..., f k } be a Gröbner basis of I ordered so that Then T(f 0 ) < T(f 1 ) < < T(f k ). f 0 = P G 1 G k+1, f j = P H j G j+1 G k+1, 1 j < k, f k = P H k G k+1, where P is the primitive part of f 0 k[x 1 ][X 2 ]; G i k[x 1 ], 1 i k + 1; H i k[x 1 ][X 2 ] is a monic polynomial of degree d(i), for each i; d(1) < d(2) < < d(k); H i+1 (G 1 G i,..., H j G j+1 G i,..., H i 1 G i, H i ), i. 23

24 VII. Axis-of-Evil Theorem Marinari M.G., Mora T., A remark on a remark by Macaulay or Enhancing Lazard Structural Theorem. Bull. of the Iranian Math. Soc., 29 (2003), ; Marinari M.G., Mora T. Some Comments on Cerlienco Mureddu Algorithm and Enhanced Lazard Structural Theorem. Rejected by ISSAC-2004 (2004) Marinari M.G., Mora T. Cerlienco Mureddu Correpondence and Lazard Structural Theorem. Investigaciones Mathematicas (2006). To appear. 24

25 Description of the combinatorial structure [Gröbner and border basis, linear and Gröbner representation] of a 0-dimensional ideal I = q i P, q i = (X 1 a i1,, X n a in ) in terms of a Macaualy representation, i.e. of its roots (a i1,, a in ) and of the Macaulay basis of each q i. It is summarized into 22 statements. The description is algorithmical in terms of elementary combinatorial tools and linear interpolation. It extends Cerlienco Mureddu Correspondence and Lazard s Structural Theorem. The proof is essentially a direct application of Möller s Algorithm. in honour of Trythemius, the founder of cryptography (Steganographia [1500], Polygraphia [1508]) which introdiced in german the 22 th letter W in order to perform german gematria. 25

26 Let I P be a zero-dimensional radical ideal; Z := {a 1,..., a s } k n its roots; N := N(I); G < (I) := {t 1,..., t r }, t 1 < t 2 <... < t r, t i := X d(i) 1 1 X d(i) n n basis of its associated monomial ideal T < (I); the minimal G := {f 1,..., f r }, T(f i ) = t i i, the unique reduced lexicographical Gröbner basis of I. There is a combinatorial algorithm which, given Z, returns sets of points Z mδi k m, m, δ, i : 1 i r, 1 m n, 1 δ d (i) m, thus allowing to compute by means of Cerlienco Mureddu Algorithm the corresponding order ideal F mδi := N(Z mδi ) T k[x 1,..., X m 1 ] and, by interpolation unique polynomials which satisfy the relation Moreover, setting f i = m γ mδi := X m δ γ mδi ω F mδi c ω ω (mod (f 1,..., f i 1 ) i. ν the maximal value such that d (i) ν k[x 1,..., X ν ] \ k[x 1,..., X ν 1 ], ν 1 L i := m=1 δ γ mδi and 0, d (i) m = 0, m > ν so that f i P i := δ γ νδi we have f i = L i P i where L i is the leading polynomial of f i. X m (a) = ω F mδi c ω ω(a), a Z mδi. 26

De Nugis Groebnerialium 5: Noether, Macaulay, Jordan

De Nugis Groebnerialium 5: Noether, Macaulay, Jordan ACA 2018 Santiago de Compostela Re-reading Macaulay References Macaulay F. S., On the Resolution of a given Modular System into Primary Systems including