![Page 1: Bernoulli-type measures and the greedy beta-expansion · Bernoulli-type measures and the greedy beta-expansion Tuomas Sahlsten WinterSchoolonMultifractalsandNumberTheory UniversityofBremen,22.3.2013](https://reader030.vdocuments.pub/reader030/viewer/2022040118/5e183cf13557dc74c17a8bf3/html5/thumbnails/1.jpg)
Bernoulli-type measures and the greedy beta-expansion
Tuomas Sahlsten
Winter School on Multifractals and Number TheoryUniversity of Bremen, 22.3.2013
Joint work with 李兵
![Page 2: Bernoulli-type measures and the greedy beta-expansion · Bernoulli-type measures and the greedy beta-expansion Tuomas Sahlsten WinterSchoolonMultifractalsandNumberTheory UniversityofBremen,22.3.2013](https://reader030.vdocuments.pub/reader030/viewer/2022040118/5e183cf13557dc74c17a8bf3/html5/thumbnails/2.jpg)
Sidorov’s TheoremIf 1 < β < 2, then Lebesgue a.e. x ∈ [0, 1
β−1 ] has continuum β-expansions.
![Page 3: Bernoulli-type measures and the greedy beta-expansion · Bernoulli-type measures and the greedy beta-expansion Tuomas Sahlsten WinterSchoolonMultifractalsandNumberTheory UniversityofBremen,22.3.2013](https://reader030.vdocuments.pub/reader030/viewer/2022040118/5e183cf13557dc74c17a8bf3/html5/thumbnails/3.jpg)
Sidorov’s TheoremIf 1 < β < 2, then Lebesgue a.e. x ∈ [0, 1
β−1 ] has continuum β-expansions.
![Page 4: Bernoulli-type measures and the greedy beta-expansion · Bernoulli-type measures and the greedy beta-expansion Tuomas Sahlsten WinterSchoolonMultifractalsandNumberTheory UniversityofBremen,22.3.2013](https://reader030.vdocuments.pub/reader030/viewer/2022040118/5e183cf13557dc74c17a8bf3/html5/thumbnails/4.jpg)
Sidorov’s TheoremIf 1 < β < 2, then Lebesgue a.e. x ∈ [0, 1
β−1 ] has continuum β-expansions.
![Page 5: Bernoulli-type measures and the greedy beta-expansion · Bernoulli-type measures and the greedy beta-expansion Tuomas Sahlsten WinterSchoolonMultifractalsandNumberTheory UniversityofBremen,22.3.2013](https://reader030.vdocuments.pub/reader030/viewer/2022040118/5e183cf13557dc74c17a8bf3/html5/thumbnails/5.jpg)
Sidorov’s TheoremIf 1 < β < 2, then Lebesgue a.e. x ∈ [0, 1
β−1 ] has continuum β-expansions.
![Page 6: Bernoulli-type measures and the greedy beta-expansion · Bernoulli-type measures and the greedy beta-expansion Tuomas Sahlsten WinterSchoolonMultifractalsandNumberTheory UniversityofBremen,22.3.2013](https://reader030.vdocuments.pub/reader030/viewer/2022040118/5e183cf13557dc74c17a8bf3/html5/thumbnails/6.jpg)
Sidorov’s TheoremIf 1 < β < 2, then Lebesgue a.e. x ∈ [0, 1
β−1 ] has continuum β-expansions.
![Page 7: Bernoulli-type measures and the greedy beta-expansion · Bernoulli-type measures and the greedy beta-expansion Tuomas Sahlsten WinterSchoolonMultifractalsandNumberTheory UniversityofBremen,22.3.2013](https://reader030.vdocuments.pub/reader030/viewer/2022040118/5e183cf13557dc74c17a8bf3/html5/thumbnails/7.jpg)
Greedy tree
Let Σβ ⊂ {0, 1}N be the subtree of greedy expansions of numbers in [0, 1).
• The (greedy) β-shift is the dynamical system (Σβ, σβ); σβ = σ|Σβ
• Example: if β is the Golden ratio 1+√5
2 , then
Σβ = {w ∈ {0, 1}N : 11 /∈ w}
![Page 8: Bernoulli-type measures and the greedy beta-expansion · Bernoulli-type measures and the greedy beta-expansion Tuomas Sahlsten WinterSchoolonMultifractalsandNumberTheory UniversityofBremen,22.3.2013](https://reader030.vdocuments.pub/reader030/viewer/2022040118/5e183cf13557dc74c17a8bf3/html5/thumbnails/8.jpg)
Greedy tree
Let Σβ ⊂ {0, 1}N be the subtree of greedy expansions of numbers in [0, 1).
• The (greedy) β-shift is the dynamical system (Σβ, σβ); σβ = σ|Σβ
• Example: if β is the Golden ratio 1+√5
2 , then
Σβ = {w ∈ {0, 1}N : 11 /∈ w}
![Page 9: Bernoulli-type measures and the greedy beta-expansion · Bernoulli-type measures and the greedy beta-expansion Tuomas Sahlsten WinterSchoolonMultifractalsandNumberTheory UniversityofBremen,22.3.2013](https://reader030.vdocuments.pub/reader030/viewer/2022040118/5e183cf13557dc74c17a8bf3/html5/thumbnails/9.jpg)
Greedy tree
Let Σβ ⊂ {0, 1}N be the subtree of greedy expansions of numbers in [0, 1).
• The (greedy) β-shift is the dynamical system (Σβ, σβ); σβ = σ|Σβ
• Example: if β is the Golden ratio 1+√5
2 , then
Σβ = {w ∈ {0, 1}N : 11 /∈ w}
![Page 10: Bernoulli-type measures and the greedy beta-expansion · Bernoulli-type measures and the greedy beta-expansion Tuomas Sahlsten WinterSchoolonMultifractalsandNumberTheory UniversityofBremen,22.3.2013](https://reader030.vdocuments.pub/reader030/viewer/2022040118/5e183cf13557dc74c17a8bf3/html5/thumbnails/10.jpg)
Greedy tree
Let Σβ ⊂ {0, 1}N be the subtree of greedy expansions of numbers in [0, 1).
• The (greedy) β-shift is the dynamical system (Σβ, σβ); σβ = σ|Σβ
• Example: if β is the Golden ratio 1+√5
2 , then
Σβ = {w ∈ {0, 1}N : 11 /∈ w}
![Page 11: Bernoulli-type measures and the greedy beta-expansion · Bernoulli-type measures and the greedy beta-expansion Tuomas Sahlsten WinterSchoolonMultifractalsandNumberTheory UniversityofBremen,22.3.2013](https://reader030.vdocuments.pub/reader030/viewer/2022040118/5e183cf13557dc74c17a8bf3/html5/thumbnails/11.jpg)
Greedy tree
Let Σβ ⊂ {0, 1}N be the subtree of greedy expansions of numbers in [0, 1).
• The (greedy) β-shift is the dynamical system (Σβ, σβ); σβ = σ|Σβ
• Example: if β is the Golden ratio 1+√5
2 , then
Σβ = {w ∈ {0, 1}N : 11 /∈ w}
![Page 12: Bernoulli-type measures and the greedy beta-expansion · Bernoulli-type measures and the greedy beta-expansion Tuomas Sahlsten WinterSchoolonMultifractalsandNumberTheory UniversityofBremen,22.3.2013](https://reader030.vdocuments.pub/reader030/viewer/2022040118/5e183cf13557dc74c17a8bf3/html5/thumbnails/12.jpg)
Aim
Besicovitch-Eggleston (multifractal) analysis for (greedy) β-expansions?
E.g. the geometry of
Fp,β = πβ
{w ∈ Σβ :
1
n
n−1∑k=0
1(wk = 0)n→∞−→ p
}?
Here πβ : {0, 1}N → [0, 1β−1 ] is the projection πβ(w) =
∑wiβ
−i.
Theorem (Pfister, Sullivan 2005)
dimHFp,β = sup{hµ(σβ)
log β: σβµ = µ, µ[0] = p
}
• If (Σβ, σβ) is of finite type (i.e. 1 = ε1β−1 + · · ·+ εMβ
−M ), we havethermodynamical formalism at our disposal (Fan, Feng, Wu ’01)...
...so we are done? What if (Σβ, σβ) is not SFT?
![Page 13: Bernoulli-type measures and the greedy beta-expansion · Bernoulli-type measures and the greedy beta-expansion Tuomas Sahlsten WinterSchoolonMultifractalsandNumberTheory UniversityofBremen,22.3.2013](https://reader030.vdocuments.pub/reader030/viewer/2022040118/5e183cf13557dc74c17a8bf3/html5/thumbnails/13.jpg)
AimBesicovitch-Eggleston (multifractal) analysis for (greedy) β-expansions?
E.g. the geometry of
Fp,β = πβ
{w ∈ Σβ :
1
n
n−1∑k=0
1(wk = 0)n→∞−→ p
}?
Here πβ : {0, 1}N → [0, 1β−1 ] is the projection πβ(w) =
∑wiβ
−i.
Theorem (Pfister, Sullivan 2005)
dimHFp,β = sup{hµ(σβ)
log β: σβµ = µ, µ[0] = p
}
• If (Σβ, σβ) is of finite type (i.e. 1 = ε1β−1 + · · ·+ εMβ
−M ), we havethermodynamical formalism at our disposal (Fan, Feng, Wu ’01)...
...so we are done? What if (Σβ, σβ) is not SFT?
![Page 14: Bernoulli-type measures and the greedy beta-expansion · Bernoulli-type measures and the greedy beta-expansion Tuomas Sahlsten WinterSchoolonMultifractalsandNumberTheory UniversityofBremen,22.3.2013](https://reader030.vdocuments.pub/reader030/viewer/2022040118/5e183cf13557dc74c17a8bf3/html5/thumbnails/14.jpg)
AimBesicovitch-Eggleston (multifractal) analysis for (greedy) β-expansions?
E.g. the geometry of
Fp,β = πβ
{w ∈ Σβ :
1
n
n−1∑k=0
1(wk = 0)n→∞−→ p
}?
Here πβ : {0, 1}N → [0, 1β−1 ] is the projection πβ(w) =
∑wiβ
−i.
Theorem (Pfister, Sullivan 2005)
dimHFp,β = sup{hµ(σβ)
log β: σβµ = µ, µ[0] = p
}
• If (Σβ, σβ) is of finite type (i.e. 1 = ε1β−1 + · · ·+ εMβ
−M ), we havethermodynamical formalism at our disposal (Fan, Feng, Wu ’01)...
...so we are done? What if (Σβ, σβ) is not SFT?
![Page 15: Bernoulli-type measures and the greedy beta-expansion · Bernoulli-type measures and the greedy beta-expansion Tuomas Sahlsten WinterSchoolonMultifractalsandNumberTheory UniversityofBremen,22.3.2013](https://reader030.vdocuments.pub/reader030/viewer/2022040118/5e183cf13557dc74c17a8bf3/html5/thumbnails/15.jpg)
AimBesicovitch-Eggleston (multifractal) analysis for (greedy) β-expansions?
E.g. the geometry of
Fp,β = πβ
{w ∈ Σβ :
1
n
n−1∑k=0
1(wk = 0)n→∞−→ p
}?
Here πβ : {0, 1}N → [0, 1β−1 ] is the projection πβ(w) =
∑wiβ
−i.
Theorem (Pfister, Sullivan 2005)
dimHFp,β = sup{hµ(σβ)
log β: σβµ = µ, µ[0] = p
}
• If (Σβ, σβ) is of finite type (i.e. 1 = ε1β−1 + · · ·+ εMβ
−M ), we havethermodynamical formalism at our disposal (Fan, Feng, Wu ’01)...
...so we are done? What if (Σβ, σβ) is not SFT?
![Page 16: Bernoulli-type measures and the greedy beta-expansion · Bernoulli-type measures and the greedy beta-expansion Tuomas Sahlsten WinterSchoolonMultifractalsandNumberTheory UniversityofBremen,22.3.2013](https://reader030.vdocuments.pub/reader030/viewer/2022040118/5e183cf13557dc74c17a8bf3/html5/thumbnails/16.jpg)
AimBesicovitch-Eggleston (multifractal) analysis for (greedy) β-expansions?
E.g. the geometry of
Fp,β = πβ
{w ∈ Σβ :
1
n
n−1∑k=0
1(wk = 0)n→∞−→ p
}?
Here πβ : {0, 1}N → [0, 1β−1 ] is the projection πβ(w) =
∑wiβ
−i.
Theorem (Pfister, Sullivan 2005)
dimHFp,β = sup{hµ(σβ)
log β: σβµ = µ, µ[0] = p
}
• If (Σβ, σβ) is of finite type (i.e. 1 = ε1β−1 + · · ·+ εMβ
−M ), we havethermodynamical formalism at our disposal (Fan, Feng, Wu ’01)...
...so we are done? What if (Σβ, σβ) is not SFT?
![Page 17: Bernoulli-type measures and the greedy beta-expansion · Bernoulli-type measures and the greedy beta-expansion Tuomas Sahlsten WinterSchoolonMultifractalsandNumberTheory UniversityofBremen,22.3.2013](https://reader030.vdocuments.pub/reader030/viewer/2022040118/5e183cf13557dc74c17a8bf3/html5/thumbnails/17.jpg)
AimBesicovitch-Eggleston (multifractal) analysis for (greedy) β-expansions?
E.g. the geometry of
Fp,β = πβ
{w ∈ Σβ :
1
n
n−1∑k=0
1(wk = 0)n→∞−→ p
}?
Here πβ : {0, 1}N → [0, 1β−1 ] is the projection πβ(w) =
∑wiβ
−i.
Theorem (Pfister, Sullivan 2005)
dimHFp,β = sup{hµ(σβ)
log β: σβµ = µ, µ[0] = p
}
• If (Σβ, σβ) is of finite type (i.e. 1 = ε1β−1 + · · ·+ εMβ
−M ), we havethermodynamical formalism at our disposal (Fan, Feng, Wu ’01)...
...so we are done? What if (Σβ, σβ) is not SFT?
![Page 18: Bernoulli-type measures and the greedy beta-expansion · Bernoulli-type measures and the greedy beta-expansion Tuomas Sahlsten WinterSchoolonMultifractalsandNumberTheory UniversityofBremen,22.3.2013](https://reader030.vdocuments.pub/reader030/viewer/2022040118/5e183cf13557dc74c17a8bf3/html5/thumbnails/18.jpg)
Can we follow the ideas of Besicovitch-Eggleston?
First step. Find a “Bernoulli measure” on the symbolic space Σβ .
• A ’Bernoulli-type’ measure µp:
![Page 19: Bernoulli-type measures and the greedy beta-expansion · Bernoulli-type measures and the greedy beta-expansion Tuomas Sahlsten WinterSchoolonMultifractalsandNumberTheory UniversityofBremen,22.3.2013](https://reader030.vdocuments.pub/reader030/viewer/2022040118/5e183cf13557dc74c17a8bf3/html5/thumbnails/19.jpg)
Can we follow the ideas of Besicovitch-Eggleston?
First step. Find a “Bernoulli measure” on the symbolic space Σβ .
• A ’Bernoulli-type’ measure µp:
![Page 20: Bernoulli-type measures and the greedy beta-expansion · Bernoulli-type measures and the greedy beta-expansion Tuomas Sahlsten WinterSchoolonMultifractalsandNumberTheory UniversityofBremen,22.3.2013](https://reader030.vdocuments.pub/reader030/viewer/2022040118/5e183cf13557dc74c17a8bf3/html5/thumbnails/20.jpg)
Can we follow the ideas of Besicovitch-Eggleston?
First step. Find a “Bernoulli measure” on the symbolic space Σβ .
• A ’Bernoulli-type’ measure µp:
![Page 21: Bernoulli-type measures and the greedy beta-expansion · Bernoulli-type measures and the greedy beta-expansion Tuomas Sahlsten WinterSchoolonMultifractalsandNumberTheory UniversityofBremen,22.3.2013](https://reader030.vdocuments.pub/reader030/viewer/2022040118/5e183cf13557dc74c17a8bf3/html5/thumbnails/21.jpg)
Can we follow the ideas of Besicovitch-Eggleston?
First step. Find a “Bernoulli measure” on the symbolic space Σβ .
• A ’Bernoulli-type’ measure µp:
![Page 22: Bernoulli-type measures and the greedy beta-expansion · Bernoulli-type measures and the greedy beta-expansion Tuomas Sahlsten WinterSchoolonMultifractalsandNumberTheory UniversityofBremen,22.3.2013](https://reader030.vdocuments.pub/reader030/viewer/2022040118/5e183cf13557dc74c17a8bf3/html5/thumbnails/22.jpg)
Can we follow the ideas of Besicovitch-Eggleston?
First step. Find a “Bernoulli measure” on the symbolic space Σβ .
• A ’Bernoulli-type’ measure µp:
![Page 23: Bernoulli-type measures and the greedy beta-expansion · Bernoulli-type measures and the greedy beta-expansion Tuomas Sahlsten WinterSchoolonMultifractalsandNumberTheory UniversityofBremen,22.3.2013](https://reader030.vdocuments.pub/reader030/viewer/2022040118/5e183cf13557dc74c17a8bf3/html5/thumbnails/23.jpg)
Can we follow the ideas of Besicovitch-Eggleston?
First step. Find a “Bernoulli measure” on the symbolic space Σβ .
• A ’Bernoulli-type’ measure µp:
![Page 24: Bernoulli-type measures and the greedy beta-expansion · Bernoulli-type measures and the greedy beta-expansion Tuomas Sahlsten WinterSchoolonMultifractalsandNumberTheory UniversityofBremen,22.3.2013](https://reader030.vdocuments.pub/reader030/viewer/2022040118/5e183cf13557dc74c17a8bf3/html5/thumbnails/24.jpg)
Properties of µp
• We are missing the precious independence/product structure, i.e.
σβµp 6= µp and sometimes µp[ww′] 6= µp[w]µp[w
′]...
...so no strong law of large numbers (ergodic theorem) for us /
• However, µp is ‘quasi-invariant’ in the sense that
µp � σβµp � µp
and also satisfies the ’ergodic property’
A = σ−1β A =⇒ µp(A) = 0 or 1...
...but these alone do not give us strong enough ergodic theory
![Page 25: Bernoulli-type measures and the greedy beta-expansion · Bernoulli-type measures and the greedy beta-expansion Tuomas Sahlsten WinterSchoolonMultifractalsandNumberTheory UniversityofBremen,22.3.2013](https://reader030.vdocuments.pub/reader030/viewer/2022040118/5e183cf13557dc74c17a8bf3/html5/thumbnails/25.jpg)
Properties of µp
• We are missing the precious independence/product structure, i.e.
σβµp 6= µp and sometimes µp[ww′] 6= µp[w]µp[w
′]...
...so no strong law of large numbers (ergodic theorem) for us /
• However, µp is ‘quasi-invariant’ in the sense that
µp � σβµp � µp
and also satisfies the ’ergodic property’
A = σ−1β A =⇒ µp(A) = 0 or 1...
...but these alone do not give us strong enough ergodic theory
![Page 26: Bernoulli-type measures and the greedy beta-expansion · Bernoulli-type measures and the greedy beta-expansion Tuomas Sahlsten WinterSchoolonMultifractalsandNumberTheory UniversityofBremen,22.3.2013](https://reader030.vdocuments.pub/reader030/viewer/2022040118/5e183cf13557dc74c17a8bf3/html5/thumbnails/26.jpg)
Properties of µp
• We are missing the precious independence/product structure, i.e.
σβµp 6= µp and sometimes µp[ww′] 6= µp[w]µp[w
′]...
...so no strong law of large numbers (ergodic theorem) for us /
• However, µp is ‘quasi-invariant’ in the sense that
µp � σβµp � µp
and also satisfies the ’ergodic property’
A = σ−1β A =⇒ µp(A) = 0 or 1...
...but these alone do not give us strong enough ergodic theory
![Page 27: Bernoulli-type measures and the greedy beta-expansion · Bernoulli-type measures and the greedy beta-expansion Tuomas Sahlsten WinterSchoolonMultifractalsandNumberTheory UniversityofBremen,22.3.2013](https://reader030.vdocuments.pub/reader030/viewer/2022040118/5e183cf13557dc74c17a8bf3/html5/thumbnails/27.jpg)
What is ‘enough’ then?
Quasi-product measures
A measure µ on Σβ is quasi-product (or quasi-Bernoulli), if there existsC ≥ 1 s.t.
C−1µ[w]µ[w′] ≤ µ[ww′] ≤ Cµ[w]µ[w′]
for w,w′ ∈ Σ∗β such that ww′ ∈ Σ∗β .
Unfortunately, this is too strong requirement for measures µp in general:
Theorem (Li, S. 2013)
Let 1 < β < 2 and 0 < p < 1. Then
(Σβ, σβ) is a subshift of finite type ⇐⇒ µp is quasi-product
![Page 28: Bernoulli-type measures and the greedy beta-expansion · Bernoulli-type measures and the greedy beta-expansion Tuomas Sahlsten WinterSchoolonMultifractalsandNumberTheory UniversityofBremen,22.3.2013](https://reader030.vdocuments.pub/reader030/viewer/2022040118/5e183cf13557dc74c17a8bf3/html5/thumbnails/28.jpg)
What is ‘enough’ then?
Quasi-product measures
A measure µ on Σβ is quasi-product (or quasi-Bernoulli), if there existsC ≥ 1 s.t.
C−1µ[w]µ[w′] ≤ µ[ww′] ≤ Cµ[w]µ[w′]
for w,w′ ∈ Σ∗β such that ww′ ∈ Σ∗β .
Unfortunately, this is too strong requirement for measures µp in general:
Theorem (Li, S. 2013)
Let 1 < β < 2 and 0 < p < 1. Then
(Σβ, σβ) is a subshift of finite type ⇐⇒ µp is quasi-product
![Page 29: Bernoulli-type measures and the greedy beta-expansion · Bernoulli-type measures and the greedy beta-expansion Tuomas Sahlsten WinterSchoolonMultifractalsandNumberTheory UniversityofBremen,22.3.2013](https://reader030.vdocuments.pub/reader030/viewer/2022040118/5e183cf13557dc74c17a8bf3/html5/thumbnails/29.jpg)
What is ‘enough’ then?
Quasi-product measures
A measure µ on Σβ is quasi-product (or quasi-Bernoulli), if there existsC ≥ 1 s.t.
C−1µ[w]µ[w′] ≤ µ[ww′] ≤ Cµ[w]µ[w′]
for w,w′ ∈ Σ∗β such that ww′ ∈ Σ∗β .
Unfortunately, this is too strong requirement for measures µp in general:
Theorem (Li, S. 2013)
Let 1 < β < 2 and 0 < p < 1. Then
(Σβ, σβ) is a subshift of finite type ⇐⇒ µp is quasi-product
![Page 30: Bernoulli-type measures and the greedy beta-expansion · Bernoulli-type measures and the greedy beta-expansion Tuomas Sahlsten WinterSchoolonMultifractalsandNumberTheory UniversityofBremen,22.3.2013](https://reader030.vdocuments.pub/reader030/viewer/2022040118/5e183cf13557dc74c17a8bf3/html5/thumbnails/30.jpg)
What is ‘enough’ then?
Quasi-product measures
A measure µ on Σβ is quasi-product (or quasi-Bernoulli), if there existsC ≥ 1 s.t.
C−1µ[w]µ[w′] ≤ µ[ww′] ≤ Cµ[w]µ[w′]
for w,w′ ∈ Σ∗β such that ww′ ∈ Σ∗β .
Unfortunately, this is too strong requirement for measures µp in general:
Theorem (Li, S. 2013)
Let 1 < β < 2 and 0 < p < 1. Then
(Σβ, σβ) is a subshift of finite type ⇐⇒ µp is quasi-product
![Page 31: Bernoulli-type measures and the greedy beta-expansion · Bernoulli-type measures and the greedy beta-expansion Tuomas Sahlsten WinterSchoolonMultifractalsandNumberTheory UniversityofBremen,22.3.2013](https://reader030.vdocuments.pub/reader030/viewer/2022040118/5e183cf13557dc74c17a8bf3/html5/thumbnails/31.jpg)
Sketch of the proof I
• Numbers for tracking branching:
N0(w) = ]{1 ≤ k ≤ |w| : wk = 0 and w1 . . . wk−11 ∈ Σ∗β};
N1(w) = ]{1 ≤ k ≤ |w| : wk = 1}.
• By definitionµp[w] = pN0(w)(1− p)N1(w)...
...and no matter how we choose β, we have
N0(ww′) ≤ N0(w) +N0(w
′) and N1(ww′) = N1(w) +N1(w
′).
• Thus
µp[ww′] � µp[w]µp[w
′] ⇐⇒ there exists M ≥ 0 withN0(ww
′) ≥ N0(w) +N0(w′)−M.
![Page 32: Bernoulli-type measures and the greedy beta-expansion · Bernoulli-type measures and the greedy beta-expansion Tuomas Sahlsten WinterSchoolonMultifractalsandNumberTheory UniversityofBremen,22.3.2013](https://reader030.vdocuments.pub/reader030/viewer/2022040118/5e183cf13557dc74c17a8bf3/html5/thumbnails/32.jpg)
Sketch of the proof I
• Numbers for tracking branching:
N0(w) = ]{1 ≤ k ≤ |w| : wk = 0 and w1 . . . wk−11 ∈ Σ∗β};
N1(w) = ]{1 ≤ k ≤ |w| : wk = 1}.
• By definitionµp[w] = pN0(w)(1− p)N1(w)...
...and no matter how we choose β, we have
N0(ww′) ≤ N0(w) +N0(w
′) and N1(ww′) = N1(w) +N1(w
′).
• Thus
µp[ww′] � µp[w]µp[w
′] ⇐⇒ there exists M ≥ 0 withN0(ww
′) ≥ N0(w) +N0(w′)−M.
![Page 33: Bernoulli-type measures and the greedy beta-expansion · Bernoulli-type measures and the greedy beta-expansion Tuomas Sahlsten WinterSchoolonMultifractalsandNumberTheory UniversityofBremen,22.3.2013](https://reader030.vdocuments.pub/reader030/viewer/2022040118/5e183cf13557dc74c17a8bf3/html5/thumbnails/33.jpg)
Sketch of the proof I
• Numbers for tracking branching:
N0(w) = ]{1 ≤ k ≤ |w| : wk = 0 and w1 . . . wk−11 ∈ Σ∗β};
N1(w) = ]{1 ≤ k ≤ |w| : wk = 1}.
• By definitionµp[w] = pN0(w)(1− p)N1(w)...
...and no matter how we choose β, we have
N0(ww′) ≤ N0(w) +N0(w
′) and N1(ww′) = N1(w) +N1(w
′).
• Thus
µp[ww′] � µp[w]µp[w
′] ⇐⇒ there exists M ≥ 0 withN0(ww
′) ≥ N0(w) +N0(w′)−M.
![Page 34: Bernoulli-type measures and the greedy beta-expansion · Bernoulli-type measures and the greedy beta-expansion Tuomas Sahlsten WinterSchoolonMultifractalsandNumberTheory UniversityofBremen,22.3.2013](https://reader030.vdocuments.pub/reader030/viewer/2022040118/5e183cf13557dc74c17a8bf3/html5/thumbnails/34.jpg)
Sketch of the proof I
• Numbers for tracking branching:
N0(w) = ]{1 ≤ k ≤ |w| : wk = 0 and w1 . . . wk−11 ∈ Σ∗β};
N1(w) = ]{1 ≤ k ≤ |w| : wk = 1}.
• By definitionµp[w] = pN0(w)(1− p)N1(w)...
...and no matter how we choose β, we have
N0(ww′) ≤ N0(w) +N0(w
′) and N1(ww′) = N1(w) +N1(w
′).
• Thus
µp[ww′] � µp[w]µp[w
′] ⇐⇒ there exists M ≥ 0 withN0(ww
′) ≥ N0(w) +N0(w′)−M.
![Page 35: Bernoulli-type measures and the greedy beta-expansion · Bernoulli-type measures and the greedy beta-expansion Tuomas Sahlsten WinterSchoolonMultifractalsandNumberTheory UniversityofBremen,22.3.2013](https://reader030.vdocuments.pub/reader030/viewer/2022040118/5e183cf13557dc74c17a8bf3/html5/thumbnails/35.jpg)
Sketch of the proof II⇐ If (Σβ, σβ) is an M -step SFT, i.e. 1 = ε1β
−1 + · · ·+ εMβ−M ,
N0(ww′) ≥ N0(w) +N0(w
′)−M.
Hence µp is quasi-product.
Lemma (Growth of N0)
For any 1 < β < 2 and w ∈ Σβ , πβ(w) 6= 1, we have
N0(w1w2 . . . wk)→∞, as k →∞.
⇒ If (Σβ, σβ) is not SFT, then 1 has infinite β-expansion ε1ε2ε3 . . ....so we can choose kn →∞ with
N0(ε2 . . . εkn) > n, n ∈ N
=⇒ N0(ε1)︸ ︷︷ ︸=0
+ N0(ε2 . . . εkn)− n > N0(ε1ε2 . . . εkn)︸ ︷︷ ︸=0
, n ∈ N.
Hence µp is not quasi-product. ‘�’
![Page 36: Bernoulli-type measures and the greedy beta-expansion · Bernoulli-type measures and the greedy beta-expansion Tuomas Sahlsten WinterSchoolonMultifractalsandNumberTheory UniversityofBremen,22.3.2013](https://reader030.vdocuments.pub/reader030/viewer/2022040118/5e183cf13557dc74c17a8bf3/html5/thumbnails/36.jpg)
Sketch of the proof II⇐ If (Σβ, σβ) is an M -step SFT, i.e. 1 = ε1β
−1 + · · ·+ εMβ−M ,
N0(ww′) ≥ N0(w) +N0(w
′)−M.
Hence µp is quasi-product.
Lemma (Growth of N0)
For any 1 < β < 2 and w ∈ Σβ , πβ(w) 6= 1, we have
N0(w1w2 . . . wk)→∞, as k →∞.
⇒ If (Σβ, σβ) is not SFT, then 1 has infinite β-expansion ε1ε2ε3 . . ....so we can choose kn →∞ with
N0(ε2 . . . εkn) > n, n ∈ N
=⇒ N0(ε1)︸ ︷︷ ︸=0
+ N0(ε2 . . . εkn)− n > N0(ε1ε2 . . . εkn)︸ ︷︷ ︸=0
, n ∈ N.
Hence µp is not quasi-product. ‘�’
![Page 37: Bernoulli-type measures and the greedy beta-expansion · Bernoulli-type measures and the greedy beta-expansion Tuomas Sahlsten WinterSchoolonMultifractalsandNumberTheory UniversityofBremen,22.3.2013](https://reader030.vdocuments.pub/reader030/viewer/2022040118/5e183cf13557dc74c17a8bf3/html5/thumbnails/37.jpg)
Sketch of the proof II⇐ If (Σβ, σβ) is an M -step SFT, i.e. 1 = ε1β
−1 + · · ·+ εMβ−M ,
N0(ww′) ≥ N0(w) +N0(w
′)−M.
Hence µp is quasi-product.
Lemma (Growth of N0)
For any 1 < β < 2 and w ∈ Σβ , πβ(w) 6= 1, we have
N0(w1w2 . . . wk)→∞, as k →∞.
⇒ If (Σβ, σβ) is not SFT, then 1 has infinite β-expansion ε1ε2ε3 . . ....so we can choose kn →∞ with
N0(ε2 . . . εkn) > n, n ∈ N
=⇒ N0(ε1)︸ ︷︷ ︸=0
+ N0(ε2 . . . εkn)− n > N0(ε1ε2 . . . εkn)︸ ︷︷ ︸=0
, n ∈ N.
Hence µp is not quasi-product. ‘�’
![Page 38: Bernoulli-type measures and the greedy beta-expansion · Bernoulli-type measures and the greedy beta-expansion Tuomas Sahlsten WinterSchoolonMultifractalsandNumberTheory UniversityofBremen,22.3.2013](https://reader030.vdocuments.pub/reader030/viewer/2022040118/5e183cf13557dc74c17a8bf3/html5/thumbnails/38.jpg)
Sketch of the proof II⇐ If (Σβ, σβ) is an M -step SFT, i.e. 1 = ε1β
−1 + · · ·+ εMβ−M ,
N0(ww′) ≥ N0(w) +N0(w
′)−M.
Hence µp is quasi-product.
Lemma (Growth of N0)
For any 1 < β < 2 and w ∈ Σβ , πβ(w) 6= 1, we have
N0(w1w2 . . . wk)→∞, as k →∞.
⇒ If (Σβ, σβ) is not SFT, then 1 has infinite β-expansion ε1ε2ε3 . . ....so we can choose kn →∞ with
N0(ε2 . . . εkn) > n, n ∈ N
=⇒ N0(ε1)︸ ︷︷ ︸=0
+ N0(ε2 . . . εkn)− n > N0(ε1ε2 . . . εkn)︸ ︷︷ ︸=0
, n ∈ N.
Hence µp is not quasi-product. ‘�’
![Page 39: Bernoulli-type measures and the greedy beta-expansion · Bernoulli-type measures and the greedy beta-expansion Tuomas Sahlsten WinterSchoolonMultifractalsandNumberTheory UniversityofBremen,22.3.2013](https://reader030.vdocuments.pub/reader030/viewer/2022040118/5e183cf13557dc74c17a8bf3/html5/thumbnails/39.jpg)
Sketch of the proof II⇐ If (Σβ, σβ) is an M -step SFT, i.e. 1 = ε1β
−1 + · · ·+ εMβ−M ,
N0(ww′) ≥ N0(w) +N0(w
′)−M.
Hence µp is quasi-product.
Lemma (Growth of N0)
For any 1 < β < 2 and w ∈ Σβ , πβ(w) 6= 1, we have
N0(w1w2 . . . wk)→∞, as k →∞.
⇒ If (Σβ, σβ) is not SFT, then 1 has infinite β-expansion ε1ε2ε3 . . .
...so we can choose kn →∞ with
N0(ε2 . . . εkn) > n, n ∈ N
=⇒ N0(ε1)︸ ︷︷ ︸=0
+ N0(ε2 . . . εkn)− n > N0(ε1ε2 . . . εkn)︸ ︷︷ ︸=0
, n ∈ N.
Hence µp is not quasi-product. ‘�’
![Page 40: Bernoulli-type measures and the greedy beta-expansion · Bernoulli-type measures and the greedy beta-expansion Tuomas Sahlsten WinterSchoolonMultifractalsandNumberTheory UniversityofBremen,22.3.2013](https://reader030.vdocuments.pub/reader030/viewer/2022040118/5e183cf13557dc74c17a8bf3/html5/thumbnails/40.jpg)
Sketch of the proof II⇐ If (Σβ, σβ) is an M -step SFT, i.e. 1 = ε1β
−1 + · · ·+ εMβ−M ,
N0(ww′) ≥ N0(w) +N0(w
′)−M.
Hence µp is quasi-product.
Lemma (Growth of N0)
For any 1 < β < 2 and w ∈ Σβ , πβ(w) 6= 1, we have
N0(w1w2 . . . wk)→∞, as k →∞.
⇒ If (Σβ, σβ) is not SFT, then 1 has infinite β-expansion ε1ε2ε3 . . ....so we can choose kn →∞ with
N0(ε2 . . . εkn) > n, n ∈ N
=⇒ N0(ε1)︸ ︷︷ ︸=0
+ N0(ε2 . . . εkn)− n > N0(ε1ε2 . . . εkn)︸ ︷︷ ︸=0
, n ∈ N.
Hence µp is not quasi-product. ‘�’
![Page 41: Bernoulli-type measures and the greedy beta-expansion · Bernoulli-type measures and the greedy beta-expansion Tuomas Sahlsten WinterSchoolonMultifractalsandNumberTheory UniversityofBremen,22.3.2013](https://reader030.vdocuments.pub/reader030/viewer/2022040118/5e183cf13557dc74c17a8bf3/html5/thumbnails/41.jpg)
Sketch of the proof II⇐ If (Σβ, σβ) is an M -step SFT, i.e. 1 = ε1β
−1 + · · ·+ εMβ−M ,
N0(ww′) ≥ N0(w) +N0(w
′)−M.
Hence µp is quasi-product.
Lemma (Growth of N0)
For any 1 < β < 2 and w ∈ Σβ , πβ(w) 6= 1, we have
N0(w1w2 . . . wk)→∞, as k →∞.
⇒ If (Σβ, σβ) is not SFT, then 1 has infinite β-expansion ε1ε2ε3 . . ....so we can choose kn →∞ with
N0(ε2 . . . εkn) > n, n ∈ N
=⇒ N0(ε1)︸ ︷︷ ︸=0
+ N0(ε2 . . . εkn)− n > N0(ε1ε2 . . . εkn)︸ ︷︷ ︸=0
, n ∈ N.
Hence µp is not quasi-product. ‘�’
![Page 42: Bernoulli-type measures and the greedy beta-expansion · Bernoulli-type measures and the greedy beta-expansion Tuomas Sahlsten WinterSchoolonMultifractalsandNumberTheory UniversityofBremen,22.3.2013](https://reader030.vdocuments.pub/reader030/viewer/2022040118/5e183cf13557dc74c17a8bf3/html5/thumbnails/42.jpg)
Sketch of the proof II⇐ If (Σβ, σβ) is an M -step SFT, i.e. 1 = ε1β
−1 + · · ·+ εMβ−M ,
N0(ww′) ≥ N0(w) +N0(w
′)−M.
Hence µp is quasi-product.
Lemma (Growth of N0)
For any 1 < β < 2 and w ∈ Σβ , πβ(w) 6= 1, we have
N0(w1w2 . . . wk)→∞, as k →∞.
⇒ If (Σβ, σβ) is not SFT, then 1 has infinite β-expansion ε1ε2ε3 . . ....so we can choose kn →∞ with
N0(ε2 . . . εkn) > n, n ∈ N
=⇒ N0(ε1)︸ ︷︷ ︸=0
+ N0(ε2 . . . εkn)− n > N0(ε1ε2 . . . εkn)︸ ︷︷ ︸=0
, n ∈ N.
Hence µp is not quasi-product. ‘�’
![Page 43: Bernoulli-type measures and the greedy beta-expansion · Bernoulli-type measures and the greedy beta-expansion Tuomas Sahlsten WinterSchoolonMultifractalsandNumberTheory UniversityofBremen,22.3.2013](https://reader030.vdocuments.pub/reader030/viewer/2022040118/5e183cf13557dc74c17a8bf3/html5/thumbnails/43.jpg)
The next step?
• (Σβ, σβ) is SFT ⇐⇒ there exists a unique σβ invariant ergodicmeasure µ′p equivalent to µp? (this is what we actually fear)• What is the structure of µp measures when using ‘lazier’ β-expansions
to construct the tree Σβ?• When is the projection πβµp abs. cont. to Lebesgue measure on [0, 1]?
Conjecture (A.-H. Fan 2012, personal discussion):(a) ∀β ∈ (1, 2) ∃ unique p ∈ (0, 1) s.t. πβµp � L,(b) ∀p ∈ (0, 1) ∃ unique β ∈ (1, 2) s.t. πβµp � L.
![Page 44: Bernoulli-type measures and the greedy beta-expansion · Bernoulli-type measures and the greedy beta-expansion Tuomas Sahlsten WinterSchoolonMultifractalsandNumberTheory UniversityofBremen,22.3.2013](https://reader030.vdocuments.pub/reader030/viewer/2022040118/5e183cf13557dc74c17a8bf3/html5/thumbnails/44.jpg)
The next step?
• (Σβ, σβ) is SFT ⇐⇒ there exists a unique σβ invariant ergodicmeasure µ′p equivalent to µp? (this is what we actually fear)
• What is the structure of µp measures when using ‘lazier’ β-expansionsto construct the tree Σβ?• When is the projection πβµp abs. cont. to Lebesgue measure on [0, 1]?
Conjecture (A.-H. Fan 2012, personal discussion):(a) ∀β ∈ (1, 2) ∃ unique p ∈ (0, 1) s.t. πβµp � L,(b) ∀p ∈ (0, 1) ∃ unique β ∈ (1, 2) s.t. πβµp � L.
![Page 45: Bernoulli-type measures and the greedy beta-expansion · Bernoulli-type measures and the greedy beta-expansion Tuomas Sahlsten WinterSchoolonMultifractalsandNumberTheory UniversityofBremen,22.3.2013](https://reader030.vdocuments.pub/reader030/viewer/2022040118/5e183cf13557dc74c17a8bf3/html5/thumbnails/45.jpg)
The next step?
• (Σβ, σβ) is SFT ⇐⇒ there exists a unique σβ invariant ergodicmeasure µ′p equivalent to µp? (this is what we actually fear)• What is the structure of µp measures when using ‘lazier’ β-expansions
to construct the tree Σβ?
• When is the projection πβµp abs. cont. to Lebesgue measure on [0, 1]?
Conjecture (A.-H. Fan 2012, personal discussion):(a) ∀β ∈ (1, 2) ∃ unique p ∈ (0, 1) s.t. πβµp � L,(b) ∀p ∈ (0, 1) ∃ unique β ∈ (1, 2) s.t. πβµp � L.
![Page 46: Bernoulli-type measures and the greedy beta-expansion · Bernoulli-type measures and the greedy beta-expansion Tuomas Sahlsten WinterSchoolonMultifractalsandNumberTheory UniversityofBremen,22.3.2013](https://reader030.vdocuments.pub/reader030/viewer/2022040118/5e183cf13557dc74c17a8bf3/html5/thumbnails/46.jpg)
The next step?
• (Σβ, σβ) is SFT ⇐⇒ there exists a unique σβ invariant ergodicmeasure µ′p equivalent to µp? (this is what we actually fear)• What is the structure of µp measures when using ‘lazier’ β-expansions
to construct the tree Σβ?• When is the projection πβµp abs. cont. to Lebesgue measure on [0, 1]?
Conjecture (A.-H. Fan 2012, personal discussion):(a) ∀β ∈ (1, 2) ∃ unique p ∈ (0, 1) s.t. πβµp � L,(b) ∀p ∈ (0, 1) ∃ unique β ∈ (1, 2) s.t. πβµp � L.
![Page 47: Bernoulli-type measures and the greedy beta-expansion · Bernoulli-type measures and the greedy beta-expansion Tuomas Sahlsten WinterSchoolonMultifractalsandNumberTheory UniversityofBremen,22.3.2013](https://reader030.vdocuments.pub/reader030/viewer/2022040118/5e183cf13557dc74c17a8bf3/html5/thumbnails/47.jpg)
The next step?
• (Σβ, σβ) is SFT ⇐⇒ there exists a unique σβ invariant ergodicmeasure µ′p equivalent to µp? (this is what we actually fear)• What is the structure of µp measures when using ‘lazier’ β-expansions
to construct the tree Σβ?• When is the projection πβµp abs. cont. to Lebesgue measure on [0, 1]?
Conjecture (A.-H. Fan 2012, personal discussion):(a) ∀β ∈ (1, 2) ∃ unique p ∈ (0, 1) s.t. πβµp � L,(b) ∀p ∈ (0, 1) ∃ unique β ∈ (1, 2) s.t. πβµp � L.
![Page 48: Bernoulli-type measures and the greedy beta-expansion · Bernoulli-type measures and the greedy beta-expansion Tuomas Sahlsten WinterSchoolonMultifractalsandNumberTheory UniversityofBremen,22.3.2013](https://reader030.vdocuments.pub/reader030/viewer/2022040118/5e183cf13557dc74c17a8bf3/html5/thumbnails/48.jpg)
Bernoulli convolution
![Page 49: Bernoulli-type measures and the greedy beta-expansion · Bernoulli-type measures and the greedy beta-expansion Tuomas Sahlsten WinterSchoolonMultifractalsandNumberTheory UniversityofBremen,22.3.2013](https://reader030.vdocuments.pub/reader030/viewer/2022040118/5e183cf13557dc74c17a8bf3/html5/thumbnails/49.jpg)
Bernoulli convolution
![Page 50: Bernoulli-type measures and the greedy beta-expansion · Bernoulli-type measures and the greedy beta-expansion Tuomas Sahlsten WinterSchoolonMultifractalsandNumberTheory UniversityofBremen,22.3.2013](https://reader030.vdocuments.pub/reader030/viewer/2022040118/5e183cf13557dc74c17a8bf3/html5/thumbnails/50.jpg)
Bernoulli convolution
![Page 51: Bernoulli-type measures and the greedy beta-expansion · Bernoulli-type measures and the greedy beta-expansion Tuomas Sahlsten WinterSchoolonMultifractalsandNumberTheory UniversityofBremen,22.3.2013](https://reader030.vdocuments.pub/reader030/viewer/2022040118/5e183cf13557dc74c17a8bf3/html5/thumbnails/51.jpg)
Bernoulli convolution
![Page 52: Bernoulli-type measures and the greedy beta-expansion · Bernoulli-type measures and the greedy beta-expansion Tuomas Sahlsten WinterSchoolonMultifractalsandNumberTheory UniversityofBremen,22.3.2013](https://reader030.vdocuments.pub/reader030/viewer/2022040118/5e183cf13557dc74c17a8bf3/html5/thumbnails/52.jpg)
Bernoulli convolution