Ramanujan's continued fractions of order sixteen
TheoremWeighted Lambert series for the continued fractions of order sixteen#●ready to prove
Write \((a; q)_\infty = \prod_{n \ge 0} (1 - a q^n)\), \((a_1, \dots, a_k; q)_\infty = (a_1; q)_\infty \cdots (a_k; q)_\infty\) and \(f_k = (q^k; q^k)_\infty\). For every complex number \(q\) with \(|q| < 1\),
and
MetaMathlibExt.lambert_order_sixteen_weight_n · 15 lines
public theorem_wanted lambert_order_sixteen_weight_n (q : ℂ) (hq : ‖q‖ < 1) :
(∑' n : ℕ, ((n : ℂ) + 1) *
(q ^ (n + 1) - q ^ (7 * (n + 1)) - q ^ (9 * (n + 1)) + q ^ (15 * (n + 1))) /
(1 - q ^ (16 * (n + 1)))) =
q * qPochhammerInfRaw (q ^ 16) (q ^ 16) ^ 2 * qPochhammerInfRaw (q ^ 8) (q ^ 8) ^ 2 *
(qPochhammerInfRaw (q ^ 6) (q ^ 16) * qPochhammerInfRaw (q ^ 10) (q ^ 16)) /
(qPochhammerInfRaw q (q ^ 16) * qPochhammerInfRaw (q ^ 7) (q ^ 16) *
qPochhammerInfRaw (q ^ 9) (q ^ 16) * qPochhammerInfRaw (q ^ 15) (q ^ 16)) ^ 2 ∧
(∑' n : ℕ, ((n : ℂ) + 1) *
(q ^ (3 * (n + 1)) - q ^ (5 * (n + 1)) - q ^ (11 * (n + 1)) + q ^ (13 * (n + 1))) /
(1 - q ^ (16 * (n + 1)))) =
q ^ 3 * qPochhammerInfRaw (q ^ 16) (q ^ 16) ^ 2 * qPochhammerInfRaw (q ^ 8) (q ^ 8) ^ 2 *
(qPochhammerInfRaw (q ^ 2) (q ^ 16) * qPochhammerInfRaw (q ^ 14) (q ^ 16)) /
(qPochhammerInfRaw (q ^ 3) (q ^ 16) * qPochhammerInfRaw (q ^ 5) (q ^ 16) *
qPochhammerInfRaw (q ^ 11) (q ^ 16) * qPochhammerInfRaw (q ^ 13) (q ^ 16)) ^ 2
noncomputable def qPochhammerInfRaw (a q : ℂ) : ℂ :=
tprod (fun n : ℕ => (1 - a * q ^ n))
MathlibExt/Analysis/SpecialFunctions/QPochhammer.lean:47
Sources
- A. Vanitha, Nasser Abdo Saeed Bulkhali, and M. P. Chaudhary, On a Ramanujan’s Continued Fraction of Order Sixteen and New Eisenstein Series Identities, INTEGERS 25 (2025), Article A16, Theorem 3, Equations (62)-(63).
Uses 1
TheoremLambert series of order sixteen twisted by the Legendre symbol modulo \(3\)#●ready to prove
Write \((a; q)_\infty = \prod_{n \ge 0} (1 - a q^n)\), \((a_1, \dots, a_k; q)_\infty = (a_1; q)_\infty \cdots (a_k; q)_\infty\) and \(f_k = (q^k; q^k)_\infty\), and let \(\left(\frac{n}{3}\right)\) be the Legendre symbol modulo \(3\). For every complex number \(q\) with \(|q| < 1\),
and
MetaMathlibExt.lambert_order_sixteen_legendre_three · 21 lines
public theorem_wanted lambert_order_sixteen_legendre_three (q : ℂ) (hq : ‖q‖ < 1) :
(∑' n : ℕ, (jacobiSym ((n : ℤ) + 1) 3 : ℂ) *
(q ^ (n + 1) - q ^ (7 * (n + 1)) - q ^ (9 * (n + 1)) + q ^ (15 * (n + 1))) /
(1 - q ^ (16 * (n + 1)))) =
q * qPochhammerInfRaw (q ^ 8) (q ^ 8) ^ 2 * qPochhammerInfRaw (q ^ 48) (q ^ 48) *
(qPochhammerInfRaw (q ^ 6) (q ^ 16) * qPochhammerInfRaw (q ^ 10) (q ^ 16)) *
(qPochhammerInfRaw q (q ^ 16) * qPochhammerInfRaw (q ^ 7) (q ^ 16) *
qPochhammerInfRaw (q ^ 9) (q ^ 16) * qPochhammerInfRaw (q ^ 15) (q ^ 16)) /
(qPochhammerInfRaw (q ^ 16) (q ^ 16) *
(qPochhammerInfRaw (q ^ 3) (q ^ 48) * qPochhammerInfRaw (q ^ 21) (q ^ 48) *
qPochhammerInfRaw (q ^ 27) (q ^ 48) * qPochhammerInfRaw (q ^ 45) (q ^ 48))) ∧
(∑' n : ℕ, (jacobiSym ((n : ℤ) + 1) 3 : ℂ) *
(q ^ (3 * (n + 1)) - q ^ (5 * (n + 1)) - q ^ (11 * (n + 1)) + q ^ (13 * (n + 1))) /
(1 - q ^ (16 * (n + 1)))) =
q ^ 3 * qPochhammerInfRaw (q ^ 8) (q ^ 8) ^ 2 * qPochhammerInfRaw (q ^ 48) (q ^ 48) *
(qPochhammerInfRaw (q ^ 2) (q ^ 16) * qPochhammerInfRaw (q ^ 14) (q ^ 16)) *
(qPochhammerInfRaw (q ^ 3) (q ^ 16) * qPochhammerInfRaw (q ^ 5) (q ^ 16) *
qPochhammerInfRaw (q ^ 11) (q ^ 16) * qPochhammerInfRaw (q ^ 13) (q ^ 16)) /
(qPochhammerInfRaw (q ^ 16) (q ^ 16) *
(qPochhammerInfRaw (q ^ 9) (q ^ 48) * qPochhammerInfRaw (q ^ 15) (q ^ 48) *
qPochhammerInfRaw (q ^ 33) (q ^ 48) * qPochhammerInfRaw (q ^ 39) (q ^ 48)))
noncomputable def qPochhammerInfRaw (a q : ℂ) : ℂ :=
tprod (fun n : ℕ => (1 - a * q ^ n))
MathlibExt/Analysis/SpecialFunctions/QPochhammer.lean:47
Sources
- A. Vanitha, Nasser Abdo Saeed Bulkhali, and M. P. Chaudhary, On a Ramanujan’s Continued Fraction of Order Sixteen and New Eisenstein Series Identities, INTEGERS 25 (2025), Article A16, Theorem 4, Equations (64)-(65).
Uses 1
TheoremProduct forms of Ramanujan's theta functions \(\psi\), \(f\) and \(\chi\)#●ready to prove
Write \((a; q)_\infty = \prod_{n \ge 0} (1 - a q^n)\) and \(f_k = (q^k; q^k)_\infty\), and let \(f(a, b) = \sum_{n \in \mathbb{Z}} a^{n(n+1)/2} b^{n(n-1)/2}\) be Ramanujan's general theta function. For every complex number \(q\) with \(|q| < 1\), \(f(q, q^3) = f_2^2 / f_1\), \(f(q, -q^2) = f_2^3 / (f_1 f_4)\), \((-q; q^2)_\infty = f_2^2 / (f_1 f_4)\) and \((q; q^2)_\infty = f_1 / f_2\).
In Ramanujan's notation (Berndt, Part III, Chapter 16), with \(\psi(q) = f(q, q^3)\), \(f(q) = f(q, -q^2)\) and \(\chi(q) = (-q; q^2)_\infty\), these read \(\psi(q) = f_2^2 / f_1\), \(f(q) = f_2^3 / (f_1 f_4)\), \(\chi(q) = f_2^2 / (f_1 f_4)\) and \(\chi(-q) = f_1 / f_2\).
public theorem_wanted ramanujan_psi_f_chi_eq_qPochhammer (q : ℂ) (hq : ‖q‖ < 1) :
ramanujanThetaRaw q (q ^ 3) =
qPochhammerInfRaw (q ^ 2) (q ^ 2) ^ 2 / qPochhammerInfRaw q q ∧
ramanujanThetaRaw q (-q ^ 2) =
qPochhammerInfRaw (q ^ 2) (q ^ 2) ^ 3 /
(qPochhammerInfRaw q q * qPochhammerInfRaw (q ^ 4) (q ^ 4)) ∧
qPochhammerInfRaw (-q) (q ^ 2) =
qPochhammerInfRaw (q ^ 2) (q ^ 2) ^ 2 /
(qPochhammerInfRaw q q * qPochhammerInfRaw (q ^ 4) (q ^ 4)) ∧
qPochhammerInfRaw q (q ^ 2) = qPochhammerInfRaw q q / qPochhammerInfRaw (q ^ 2) (q ^ 2)
noncomputable def ramanujanThetaRaw (a b : ℂ) : ℂ :=
∑' n : ℤ, ramanujanThetaTerm a b n
MathlibExt/NumberTheory/ModularForms/JacobiTheta/Ramanujan.lean:57
noncomputable def qPochhammerInfRaw (a q : ℂ) : ℂ :=
tprod (fun n : ℕ => (1 - a * q ^ n))
MathlibExt/Analysis/SpecialFunctions/QPochhammer.lean:47
Sources
- A. Vanitha, Nasser Abdo Saeed Bulkhali, and M. P. Chaudhary, On a Ramanujan’s Continued Fraction of Order Sixteen and New Eisenstein Series Identities, INTEGERS 25 (2025), Article A16, Lemma 1.
Uses 2
TheoremRamanujan's Entry 30 (i)–(iii) for the general theta function#●ready to prove
Let \(f(a, b) = \sum_{n \in \mathbb{Z}} a^{n(n+1)/2} b^{n(n-1)/2}\) be Ramanujan's general theta function and \(\psi(q) = f(q, q^3)\). For all complex numbers \(a\) and \(b\) with \(|ab| < 1\), \(f(a, ab^2) f(b, a^2 b) = f(a, b) \psi(ab)\) and \(f(a, b) + f(-a, -b) = 2 f(a^3 b, a b^3)\), and if moreover \(a \ne 0\), then \(f(a, b) - f(-a, -b) = 2a f(b/a, a^5 b^3)\).
public theorem_wanted ramanujanTheta_entry30 (a b : ℂ) (hab : ‖a * b‖ < 1) :
ramanujanThetaRaw a (a * b ^ 2) * ramanujanThetaRaw b (a ^ 2 * b) =
ramanujanThetaRaw a b * ramanujanThetaRaw (a * b) ((a * b) ^ 3) ∧
ramanujanThetaRaw a b + ramanujanThetaRaw (-a) (-b) =
2 * ramanujanThetaRaw (a ^ 3 * b) (a * b ^ 3) ∧
(a ≠ 0 → ramanujanThetaRaw a b - ramanujanThetaRaw (-a) (-b) =
2 * a * ramanujanThetaRaw (b / a) (a ^ 5 * b ^ 3))
noncomputable def ramanujanThetaRaw (a b : ℂ) : ℂ :=
∑' n : ℤ, ramanujanThetaTerm a b n
MathlibExt/NumberTheory/ModularForms/JacobiTheta/Ramanujan.lean:57
Sources
- A. Vanitha, Nasser Abdo Saeed Bulkhali, and M. P. Chaudhary, On a Ramanujan’s Continued Fraction of Order Sixteen and New Eisenstein Series Identities, INTEGERS 25 (2025), Article A16, Lemma 1 record, quoting Berndt, Part III, Entry 30 (i)-(iii).
Uses 1
TheoremOdd Lambert series for Ramanujan's continued fractions of order sixteen#●ready to prove
Write \((a; q)_\infty = \prod_{n \ge 0} (1 - a q^n)\) and \((a, b; q)_\infty = (a; q)_\infty (b; q)_\infty\). For a complex number \(q\) with \(|q| < 1\), put \(S(a, b) = \sum_{k \ge 0} (q^{a(2k+1)} + q^{b(2k+1)}) / (1 - q^{16(2k+1)})\), a sum over the odd multiples \(n = 2k + 1\), and \(E = q^4 (q^{32}; q^{32})_\infty^4 / (q^{16}; q^{16})_\infty^2\), \(I_1 = q (q^6, q^{26}; q^{32})_\infty / (q^{10}, q^{22}; q^{32})_\infty\) and \(I_2 = q^3 (q^2, q^{30}; q^{32})_\infty / (q^{14}, q^{18}; q^{32})_\infty\). Then \(S(3, 5) - S(11, 13) = E (I_1 + 1/I_1)\) and \(S(1, 7) - S(9, 15) = E (I_2 + 1/I_2)\). At \(q = 0\), where \(I_1 = I_2 = 0\), the quotients \(1/I_1\) and \(1/I_2\) are read as \(0\) and both sides of each identity are \(0\).
Here \(I_1\) and \(I_2\) are \(I_1(q^2)\) and \(I_2(q^2)\) for Ramanujan's continued fractions of order sixteen \(I_1(q) = q^{1/2} (q^3, q^{13}; q^{16})_\infty / (q^5, q^{11}; q^{16})_\infty\) and \(I_2(q) = q^{3/2} (q, q^{15}; q^{16})_\infty / (q^7, q^9; q^{16})_\infty\), and \(E\) is the eta quotient \(\eta^4(32\tau) / \eta^2(16\tau)\) for \(q = e^{2 \pi i \tau}\), where \(\eta(\tau) = q^{1/24} (q; q)_\infty\).
public theorem_wanted lambert_odd_order_sixteen_eq_continuedFraction (q : ℂ) (hq : ‖q‖ < 1) :
let E : ℂ := q ^ 4 * qPochhammerInfRaw (q ^ 32) (q ^ 32) ^ 4 /
qPochhammerInfRaw (q ^ 16) (q ^ 16) ^ 2
let I₁ : ℂ := q * (qPochhammerInfRaw (q ^ 6) (q ^ 32) * qPochhammerInfRaw (q ^ 26) (q ^ 32)) /
(qPochhammerInfRaw (q ^ 10) (q ^ 32) * qPochhammerInfRaw (q ^ 22) (q ^ 32))
let I₂ : ℂ := q ^ 3 *
(qPochhammerInfRaw (q ^ 2) (q ^ 32) * qPochhammerInfRaw (q ^ 30) (q ^ 32)) /
(qPochhammerInfRaw (q ^ 14) (q ^ 32) * qPochhammerInfRaw (q ^ 18) (q ^ 32))
(∑' k : ℕ, (q ^ (3 * (2 * k + 1)) + q ^ (5 * (2 * k + 1))) / (1 - q ^ (16 * (2 * k + 1))) -
∑' k : ℕ, (q ^ (11 * (2 * k + 1)) + q ^ (13 * (2 * k + 1))) /
(1 - q ^ (16 * (2 * k + 1)))) = E * (I₁ + 1 / I₁) ∧
(∑' k : ℕ, (q ^ (2 * k + 1) + q ^ (7 * (2 * k + 1))) / (1 - q ^ (16 * (2 * k + 1))) -
∑' k : ℕ, (q ^ (9 * (2 * k + 1)) + q ^ (15 * (2 * k + 1))) /
(1 - q ^ (16 * (2 * k + 1)))) = E * (I₂ + 1 / I₂)
noncomputable def qPochhammerInfRaw (a q : ℂ) : ℂ :=
tprod (fun n : ℕ => (1 - a * q ^ n))
MathlibExt/Analysis/SpecialFunctions/QPochhammer.lean:47
Sources
- A. Vanitha, Nasser Abdo Saeed Bulkhali, and M. P. Chaudhary, On a Ramanujan’s Continued Fraction of Order Sixteen and New Eisenstein Series Identities, INTEGERS 25 (2025), Article A16, Theorem 2, Equations (54)-(55).
Uses 1
DefinitionRaw Jacobi theta function \(\theta_1\)#✓fully proved
For complex numbers \(z\) and \(\tau\), the raw Jacobi theta function is
when this series is summable, and \(0\) otherwise. With \(q = e^{2 \pi i \tau}\), the factor \(e^{\pi i \tau (2n+1)^2/4}\) is \(q^{(2n+1)^2/8}\).
The value \(0\) for a non-summable series is a convention; it occurs, for example, at \(\tau = 0\) and \(z = \pi/2\). The intended object is the Jacobi theta function on the upper half-plane \(\operatorname{Im} \tau > 0\), where the series converges for every \(z\).
noncomputable def jacobiThetaOneSineRaw (z τ : ℂ) : ℂ :=
2 * ∑' n : ℕ, (-1) ^ n * Complex.exp (Real.pi * Complex.I * τ * (2 * n + 1) ^ 2 / 4) *
Complex.sin ((2 * n + 1) * z)
Sources
- A. Vanitha, Nasser Abdo Saeed Bulkhali, and M. P. Chaudhary, On a Ramanujan’s Continued Fraction of Order Sixteen and New Eisenstein Series Identities, INTEGERS 25 (2025), Article A16, Section 3, Equation (11).
Used by 1
DefinitionJacobi theta function \(\theta_1\)#✓fully proved
For complex numbers \(z\) and \(\tau\) with \(\operatorname{Im} \tau > 0\), the Jacobi theta function is
With \(q = e^{2 \pi i \tau}\), the factor \(e^{\pi i \tau (2n+1)^2/4}\) is \(q^{(2n+1)^2/8}\).
On the upper half-plane \(\operatorname{Im} \tau > 0\) the series converges for every \(z\).
noncomputable def jacobiThetaOneSine (z τ : ℂ) (_hτ : 0 < τ.im) : ℂ :=
jacobiThetaOneSineRaw z τ
noncomputable def jacobiThetaOneSineRaw (z τ : ℂ) : ℂ :=
2 * ∑' n : ℕ, (-1) ^ n * Complex.exp (Real.pi * Complex.I * τ * (2 * n + 1) ^ 2 / 4) *
Complex.sin ((2 * n + 1) * z)
WantedExt/NumberTheory/RamanujanOrderSixteenWanted.lean:171
Sources
- A. Vanitha, Nasser Abdo Saeed Bulkhali, and M. P. Chaudhary, On a Ramanujan’s Continued Fraction of Order Sixteen and New Eisenstein Series Identities, INTEGERS 25 (2025), Article A16, Section 3, Equation (11).
TheoremThe Jacobi theta function \(\theta_1\) vanishes at \(z = 0\)#✓fully proved
For every complex number \(\tau\) with \(\operatorname{Im} \tau > 0\), the Jacobi theta function satisfies \(\theta_1(0 \mid \tau) = 0\).
theorem jacobiThetaOneSine_zero (τ : ℂ) (hτ : 0 < τ.im) : jacobiThetaOneSine 0 τ hτ = 0
noncomputable def jacobiThetaOneSine (z τ : ℂ) (_hτ : 0 < τ.im) : ℂ :=
jacobiThetaOneSineRaw z τ
WantedExt/NumberTheory/RamanujanOrderSixteenWanted.lean:181
Sources
- A. Vanitha, Nasser Abdo Saeed Bulkhali, and M. P. Chaudhary, On a Ramanujan’s Continued Fraction of Order Sixteen and New Eisenstein Series Identities, INTEGERS 25 (2025), Article A16, Section 3, Equation (11).
Uses 1
TheoremOddness of the Jacobi theta function \(\theta_1\)#✓fully proved
For all complex numbers \(z\) and \(\tau\) with \(\operatorname{Im} \tau > 0\), the Jacobi theta function satisfies \(\theta_1(-z \mid \tau) = -\theta_1(z \mid \tau)\).
theorem jacobiThetaOneSine_neg (z τ : ℂ) (hτ : 0 < τ.im) :
jacobiThetaOneSine (-z) τ hτ = -jacobiThetaOneSine z τ hτ
noncomputable def jacobiThetaOneSine (z τ : ℂ) (_hτ : 0 < τ.im) : ℂ :=
jacobiThetaOneSineRaw z τ
WantedExt/NumberTheory/RamanujanOrderSixteenWanted.lean:181
Sources
- A. Vanitha, Nasser Abdo Saeed Bulkhali, and M. P. Chaudhary, On a Ramanujan’s Continued Fraction of Order Sixteen and New Eisenstein Series Identities, INTEGERS 25 (2025), Article A16, Section 3, Equation (11).
Uses 1
TheoremSine Lambert series of order sixteen as quotients of theta functions#●ready to prove
Let \(\tau\) and \(z\) be complex numbers with \(\operatorname{Im} \tau > 0\) and \(|\operatorname{Im} z| < \pi \operatorname{Im} \tau\), let \(q = e^{2 \pi i \tau}\), write \(\theta(w) = \theta_1(w \mid 16\tau)\) for the Jacobi theta function \(\theta_1\), and let \(\theta'\) be the derivative of \(\theta\). Then
and
Under these hypotheses the series converge and the denominators do not vanish.
public theorem_wanted lambert_order_sixteen_sine_eq_jacobiThetaOne (τ z : ℂ) (hτ : 0 < τ.im)
(hz : |z.im| < Real.pi * τ.im) :
let q : ℂ := Complex.exp (2 * Real.pi * Complex.I * τ)
let θ : ℂ → ℂ := fun w => jacobiThetaOneSine w (16 * τ) (by simp [hτ])
let πτ : ℂ := Real.pi * τ
(∑' n : ℕ, (q ^ (n + 1) - q ^ (7 * (n + 1)) - q ^ (9 * (n + 1)) + q ^ (15 * (n + 1))) /
(1 - q ^ (16 * (n + 1))) * Complex.sin (2 * ((n : ℂ) + 1) * z)) =
-(deriv θ 0 * θ (8 * πτ) * θ (6 * πτ) * θ (2 * z)) /
(4 * θ (z + πτ) * θ (z - πτ) * θ (z + 7 * πτ) * θ (z - 7 * πτ)) ∧
(∑' n : ℕ, (q ^ (3 * (n + 1)) - q ^ (5 * (n + 1)) - q ^ (11 * (n + 1)) +
q ^ (13 * (n + 1))) / (1 - q ^ (16 * (n + 1))) * Complex.sin (2 * ((n : ℂ) + 1) * z)) =
-(deriv θ 0 * θ (2 * πτ) * θ (8 * πτ) * θ (2 * z)) /
(4 * θ (z + 3 * πτ) * θ (z - 3 * πτ) * θ (z + 5 * πτ) * θ (z - 5 * πτ))
noncomputable def jacobiThetaOneSine (z τ : ℂ) (_hτ : 0 < τ.im) : ℂ :=
jacobiThetaOneSineRaw z τ
WantedExt/NumberTheory/RamanujanOrderSixteenWanted.lean:181
Sources
- A. Vanitha, Nasser Abdo Saeed Bulkhali, and M. P. Chaudhary, On a Ramanujan’s Continued Fraction of Order Sixteen and New Eisenstein Series Identities, INTEGERS 25 (2025), Article A16, Lemma 2 of Section 5, Equations (59)-(60).
Uses 1
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