mathlib documentation

data.polynomial.degree.trailing_degree

Trailing degree of univariate polynomials #

Main definitions #

Converts most results about degree, nat_degree and leading_coeff to results about the bottom end of a polynomial

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def polynomial.trailing_degree {R : Type u} [semiring R] (p : R[X]) :
with_top ℕ

trailing_degree p is the multiplicity of x in the polynomial p, i.e. the smallest X-exponent in p. trailing_degree p = some n when p ≠ 0 and n is the smallest power of X that appears in p, otherwise trailing_degree 0 = ⊤.

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theorem polynomial.trailing_degree_lt_wf {R : Type u} [semiring R] :
well_founded (λ (p q : R[X]), p.trailing_degree < q.trailing_degree)
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def polynomial.nat_trailing_degree {R : Type u} [semiring R] (p : R[X]) :
ℕ

nat_trailing_degree p forces trailing_degree p to ℕ, by defining nat_trailing_degree ⊤ = 0.

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def polynomial.trailing_coeff {R : Type u} [semiring R] (p : R[X]) :
R

trailing_coeff p gives the coefficient of the smallest power of X in p

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def polynomial.trailing_monic {R : Type u} [semiring R] (p : R[X]) :
Prop

a polynomial is monic_at if its trailing coefficient is 1

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theorem polynomial.trailing_monic.def {R : Type u} [semiring R] {p : R[X]} :
p.trailing_monic ↔ p.trailing_coeff = 1
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@[protected, instance]
def polynomial.trailing_monic.decidable {R : Type u} [semiring R] {p : R[X]} [decidable_eq R] :
decidable p.trailing_monic
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@[simp]
theorem polynomial.trailing_monic.trailing_coeff {R : Type u} [semiring R] {p : R[X]} (hp : p.trailing_monic) :
p.trailing_coeff = 1
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@[simp]
theorem polynomial.trailing_degree_zero {R : Type u} [semiring R] :
0.trailing_degree = ⊤
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@[simp]
theorem polynomial.trailing_coeff_zero {R : Type u} [semiring R] :
0.trailing_coeff = 0
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@[simp]
theorem polynomial.nat_trailing_degree_zero {R : Type u} [semiring R] :
0.nat_trailing_degree = 0
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theorem polynomial.trailing_degree_eq_top {R : Type u} [semiring R] {p : R[X]} :
p.trailing_degree = ⊤ ↔ p = 0
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theorem polynomial.trailing_degree_eq_nat_trailing_degree {R : Type u} [semiring R] {p : R[X]} (hp : p ≠ 0) :
p.trailing_degree = ↑(p.nat_trailing_degree)
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theorem polynomial.trailing_degree_eq_iff_nat_trailing_degree_eq {R : Type u} [semiring R] {p : R[X]} {n : ℕ} (hp : p ≠ 0) :
p.trailing_degree = ↑n ↔ p.nat_trailing_degree = n
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theorem polynomial.trailing_degree_eq_iff_nat_trailing_degree_eq_of_pos {R : Type u} [semiring R] {p : R[X]} {n : ℕ} (hn : 0 < n) :
p.trailing_degree = ↑n ↔ p.nat_trailing_degree = n
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theorem polynomial.nat_trailing_degree_eq_of_trailing_degree_eq_some {R : Type u} [semiring R] {p : R[X]} {n : ℕ} (h : p.trailing_degree = ↑n) :
p.nat_trailing_degree = n
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@[simp]
theorem polynomial.nat_trailing_degree_le_trailing_degree {R : Type u} [semiring R] {p : R[X]} :
↑(p.nat_trailing_degree) ≤ p.trailing_degree
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theorem polynomial.nat_trailing_degree_eq_of_trailing_degree_eq {R : Type u} {S : Type v} [semiring R] {p : R[X]} [semiring S] {q : S[X]} (h : p.trailing_degree = q.trailing_degree) :
p.nat_trailing_degree = q.nat_trailing_degree
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theorem polynomial.le_trailing_degree_of_ne_zero {R : Type u} {n : ℕ} [semiring R] {p : R[X]} (h : p.coeff n ≠ 0) :
p.trailing_degree ≤ ↑n
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theorem polynomial.nat_trailing_degree_le_of_ne_zero {R : Type u} {n : ℕ} [semiring R] {p : R[X]} (h : p.coeff n ≠ 0) :
p.nat_trailing_degree ≤ n
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theorem polynomial.trailing_degree_le_trailing_degree {R : Type u} [semiring R] {p q : R[X]} (h : q.coeff p.nat_trailing_degree ≠ 0) :
q.trailing_degree ≤ p.trailing_degree
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theorem polynomial.trailing_degree_ne_of_nat_trailing_degree_ne {R : Type u} [semiring R] {p : R[X]} {n : ℕ} :
p.nat_trailing_degree ≠ n → p.trailing_degree ≠ ↑n
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theorem polynomial.nat_trailing_degree_le_of_trailing_degree_le {R : Type u} [semiring R] {p : R[X]} {n : ℕ} {hp : p ≠ 0} (H : ↑n ≤ p.trailing_degree) :
n ≤ p.nat_trailing_degree
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theorem polynomial.nat_trailing_degree_le_nat_trailing_degree {R : Type u} [semiring R] {p q : R[X]} {hq : q ≠ 0} (hpq : p.trailing_degree ≤ q.trailing_degree) :
p.nat_trailing_degree ≤ q.nat_trailing_degree
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@[simp]
theorem polynomial.trailing_degree_monomial {R : Type u} {a : R} {n : ℕ} [semiring R] (ha : a ≠ 0) :
(⇑(polynomial.monomial n) a).trailing_degree = ↑n
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theorem polynomial.nat_trailing_degree_monomial {R : Type u} {a : R} {n : ℕ} [semiring R] (ha : a ≠ 0) :
(⇑(polynomial.monomial n) a).nat_trailing_degree = n
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theorem polynomial.nat_trailing_degree_monomial_le {R : Type u} {a : R} {n : ℕ} [semiring R] :
(⇑(polynomial.monomial n) a).nat_trailing_degree ≤ n
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theorem polynomial.le_trailing_degree_monomial {R : Type u} {a : R} {n : ℕ} [semiring R] :
↑n ≤ (⇑(polynomial.monomial n) a).trailing_degree
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@[simp]
theorem polynomial.trailing_degree_C {R : Type u} {a : R} [semiring R] (ha : a ≠ 0) :
(⇑polynomial.C a).trailing_degree = 0
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theorem polynomial.le_trailing_degree_C {R : Type u} {a : R} [semiring R] :
0 ≤ (⇑polynomial.C a).trailing_degree
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theorem polynomial.trailing_degree_one_le {R : Type u} [semiring R] :
0 ≤ 1.trailing_degree
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@[simp]
theorem polynomial.nat_trailing_degree_C {R : Type u} [semiring R] (a : R) :
(⇑polynomial.C a).nat_trailing_degree = 0
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@[simp]
theorem polynomial.nat_trailing_degree_one {R : Type u} [semiring R] :
1.nat_trailing_degree = 0
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@[simp]
theorem polynomial.nat_trailing_degree_nat_cast {R : Type u} [semiring R] (n : ℕ) :
↑n.nat_trailing_degree = 0
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@[simp]
theorem polynomial.trailing_degree_C_mul_X_pow {R : Type u} {a : R} [semiring R] (n : ℕ) (ha : a ≠ 0) :
((⇑polynomial.C a) * polynomial.X ^ n).trailing_degree = ↑n
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theorem polynomial.le_trailing_degree_C_mul_X_pow {R : Type u} [semiring R] (n : ℕ) (a : R) :
↑n ≤ ((⇑polynomial.C a) * polynomial.X ^ n).trailing_degree
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theorem polynomial.coeff_eq_zero_of_trailing_degree_lt {R : Type u} {n : ℕ} [semiring R] {p : R[X]} (h : ↑n < p.trailing_degree) :
p.coeff n = 0
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theorem polynomial.coeff_eq_zero_of_lt_nat_trailing_degree {R : Type u} [semiring R] {p : R[X]} {n : ℕ} (h : n < p.nat_trailing_degree) :
p.coeff n = 0
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@[simp]
theorem polynomial.coeff_nat_trailing_degree_pred_eq_zero {R : Type u} [semiring R] {p : R[X]} {hp : 0 < ↑(p.nat_trailing_degree)} :
p.coeff (p.nat_trailing_degree - 1) = 0
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theorem polynomial.le_trailing_degree_X_pow {R : Type u} [semiring R] (n : ℕ) :
↑n ≤ (polynomial.X ^ n).trailing_degree
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theorem polynomial.le_trailing_degree_X {R : Type u} [semiring R] :
1 ≤ polynomial.X.trailing_degree
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theorem polynomial.nat_trailing_degree_X_le {R : Type u} [semiring R] :
polynomial.X.nat_trailing_degree ≤ 1
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@[simp]
theorem polynomial.trailing_coeff_eq_zero {R : Type u} [semiring R] {p : R[X]} :
p.trailing_coeff = 0 ↔ p = 0
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theorem polynomial.trailing_coeff_nonzero_iff_nonzero {R : Type u} [semiring R] {p : R[X]} :
p.trailing_coeff ≠ 0 ↔ p ≠ 0
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theorem polynomial.nat_trailing_degree_mem_support_of_nonzero {R : Type u} [semiring R] {p : R[X]} :
p ≠ 0 → p.nat_trailing_degree ∈ p.support
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theorem polynomial.nat_trailing_degree_le_of_mem_supp {R : Type u} [semiring R] {p : R[X]} (a : ℕ) :
a ∈ p.support → p.nat_trailing_degree ≤ a
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theorem polynomial.nat_trailing_degree_eq_support_min' {R : Type u} [semiring R] {p : R[X]} (h : p ≠ 0) :
p.nat_trailing_degree = p.support.min' _
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theorem polynomial.nat_trailing_degree_le_nat_degree {R : Type u} [semiring R] (p : R[X]) :
p.nat_trailing_degree ≤ p.nat_degree
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theorem polynomial.nat_trailing_degree_mul_X_pow {R : Type u} [semiring R] {p : R[X]} (hp : p ≠ 0) (n : ℕ) :
(p * polynomial.X ^ n).nat_trailing_degree = p.nat_trailing_degree + n
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@[simp]
theorem polynomial.trailing_degree_one {R : Type u} [semiring R] [nontrivial R] :
1.trailing_degree = 0
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@[simp]
theorem polynomial.trailing_degree_X {R : Type u} [semiring R] [nontrivial R] :
polynomial.X.trailing_degree = 1
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@[simp]
theorem polynomial.nat_trailing_degree_X {R : Type u} [semiring R] [nontrivial R] :
polynomial.X.nat_trailing_degree = 1
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@[simp]
theorem polynomial.trailing_degree_neg {R : Type u} [ring R] (p : R[X]) :
(-p).trailing_degree = p.trailing_degree
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@[simp]
theorem polynomial.nat_trailing_degree_neg {R : Type u} [ring R] (p : R[X]) :
(-p).nat_trailing_degree = p.nat_trailing_degree
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@[simp]
theorem polynomial.nat_trailing_degree_int_cast {R : Type u} [ring R] (n : ℤ) :
↑n.nat_trailing_degree = 0
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def polynomial.next_coeff_up {R : Type u} [semiring R] (p : R[X]) :
R

The second-lowest coefficient, or 0 for constants

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@[simp]
theorem polynomial.next_coeff_up_C_eq_zero {R : Type u} [semiring R] (c : R) :
(⇑polynomial.C c).next_coeff_up = 0
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theorem polynomial.next_coeff_up_of_pos_nat_trailing_degree {R : Type u} [semiring R] (p : R[X]) (hp : 0 < p.nat_trailing_degree) :
p.next_coeff_up = p.coeff (p.nat_trailing_degree + 1)
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theorem polynomial.coeff_nat_trailing_degree_eq_zero_of_trailing_degree_lt {R : Type u} [semiring R] {p q : R[X]} (h : p.trailing_degree < q.trailing_degree) :
q.coeff p.nat_trailing_degree = 0
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theorem polynomial.ne_zero_of_trailing_degree_lt {R : Type u} [semiring R] {p : R[X]} {n : with_top ℕ} (h : p.trailing_degree < n) :
p ≠ 0