Bernoulli polynomials

The Bernoulli polynomials are an important tool obtained from Bernoulli numbers.

Mathematical overview

The $n$-th Bernoulli polynomial is defined as $$ B_n(X) = ∑_{k = 0}^n {n \choose k} (-1)^k B_k X^{n - k} $$ where $B_k$ is the $k$-th Bernoulli number. The Bernoulli polynomials are generating functions, $$ \frac{t e^{tX} }{ e^t - 1} = ∑_{n = 0}^{\infty} B_n(X) \frac{t^n}{n!} $$

Implementation detail

Bernoulli polynomials are defined using bernoulli, the Bernoulli numbers.

Main theorems

• sum_bernoulli: The sum of the $k^\mathrm{th}$ Bernoulli polynomial with binomial coefficients up to n is (n + 1) * X^n.
• Polynomial.bernoulli_generating_function: The Bernoulli polynomials act as generating functions for the exponential.

TODO

• bernoulli_eval_one_neg : $$ B_n(1 - x) = (-1)^n B_n(x) $$

def Polynomial.bernoulli (n : ℕ) : Polynomial ℚ

The Bernoulli polynomials are defined in terms of the negative Bernoulli numbers.

Equations

• Polynomial.bernoulli n = Finset.sum (Finset.range (n + 1)) fun (i : ℕ) => (Polynomial.monomial (n - i)) (bernoulli i * ↑(Nat.choose n i))

theorem Polynomial.bernoulli_def (n : ℕ) : Polynomial.bernoulli n = Finset.sum (Finset.range (n + 1)) fun (i : ℕ) => (Polynomial.monomial i) (bernoulli (n - i) * ↑(Nat.choose n i))

@[simp]

theorem Polynomial.bernoulli_zero : Polynomial.bernoulli 0 = 1

@[simp]

theorem Polynomial.bernoulli_eval_zero (n : ℕ) : Polynomial.eval 0 (Polynomial.bernoulli n) = bernoulli n

@[simp]

theorem Polynomial.bernoulli_eval_one (n : ℕ) : Polynomial.eval 1 (Polynomial.bernoulli n) = bernoulli' n

theorem Polynomial.derivative_bernoulli_add_one (k : ℕ) : Polynomial.derivative (Polynomial.bernoulli (k + 1)) = (↑k + 1) * Polynomial.bernoulli k

theorem Polynomial.derivative_bernoulli (k : ℕ) : Polynomial.derivative (Polynomial.bernoulli k) = ↑k * Polynomial.bernoulli (k - 1)

@[simp]

theorem Polynomial.sum_bernoulli (n : ℕ) : (Finset.sum (Finset.range (n + 1)) fun (k : ℕ) => ↑(Nat.choose (n + 1) k) • Polynomial.bernoulli k) = (Polynomial.monomial n) (↑n + 1)

theorem Polynomial.bernoulli_eq_sub_sum (n : ℕ) : ↑(Nat.succ n) • Polynomial.bernoulli n = (Polynomial.monomial n) ↑(Nat.succ n) - Finset.sum (Finset.range n) fun (k : ℕ) => ↑(Nat.choose (n + 1) k) • Polynomial.bernoulli k

Another version of Polynomial.sum_bernoulli.

theorem Polynomial.sum_range_pow_eq_bernoulli_sub (n : ℕ) (p : ℕ) : ((↑p + 1) * Finset.sum (Finset.range n) fun (k : ℕ) => ↑k ^ p) = Polynomial.eval (↑n) (Polynomial.bernoulli (Nat.succ p)) - bernoulli (Nat.succ p)

Another version of sum_range_pow.

theorem Polynomial.bernoulli_succ_eval (n : ℕ) (p : ℕ) : Polynomial.eval (↑n) (Polynomial.bernoulli (Nat.succ p)) = bernoulli (Nat.succ p) + (↑p + 1) * Finset.sum (Finset.range n) fun (k : ℕ) => ↑k ^ p

Rearrangement of Polynomial.sum_range_pow_eq_bernoulli_sub.

theorem Polynomial.bernoulli_eval_one_add (n : ℕ) (x : ℚ) : Polynomial.eval (1 + x) (Polynomial.bernoulli n) = Polynomial.eval x (Polynomial.bernoulli n) + ↑n * x ^ (n - 1)

theorem Polynomial.bernoulli_generating_function {A : Type u_1} [CommRing A] [Algebra ℚ A] (t : A) : (PowerSeries.mk fun (n : ℕ) => (Polynomial.aeval t) ((1 / ↑(Nat.factorial n)) • Polynomial.bernoulli n)) * (PowerSeries.exp A - 1) = PowerSeries.X * (PowerSeries.rescale t) (PowerSeries.exp A)

The theorem that $(e^X - 1) * ∑ Bₙ(t)* X^n/n! = Xe^{tX}$