A criterion for box-counting measurability John A. Rock Cal Poly Pomona [email protected]Featuring various collaborative efforts of: P. Chau, R. Giza, M. Landeros, M. Lapidus, R. Morales, C. Knox (n´ ee Sargent), K. Kurianski (n´ ee Dettmers), M. van Frankenhuijsen, E. Voskanian, K. Zaluzec, and D. Zˇ ubrini´ c. 6th Cornell Conference on Analysis, Probability, and Mathematical Physics on Fractals June 13th, 2017 John A. Rock (Cal Poly Pomona) A criterion for box-counting measurability June 13th, 2017 1 / 33
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Lapidus, van Frankenhuijsen ’97, ’06, ’13A fractal string L is a sequence of positive real numbers such that
L = (`j)∞j=1 “=” {ln : ln distinct with multiplicity mn, n ∈ N} (4)
where the lengths `j satisfy 0 < `j+1 ≤ `j ∀j and `j → 0.
The dimension DL, geometric zeta function ζL, and complex dimensionsDL of L are respectively given by
DL := inf{t ∈ R :
∑`tj <∞
}, (5)
ζL(s) :=∑
`sj =∑
mnlsn, (6)
DL(W ) := {ω ∈W ⊆ C : ζL has a pole at ω}, (7)
where Re(s) > DL and W is a suitable open region. If W = C, we writeDL for DL(W ).
John A. Rock (Cal Poly Pomona) A criterion for box-counting measurability June 13th, 2017 12 / 33
Geometric counting functions
Lapidus, van Frankenhuijsen ’97, ’06, ’13For x > 0, the geometric counting function of a fractal string L is given by
NL(x) := #{j ∈ N : `−1j ≤ x} =∑
n∈N, l−1n ≤x
mn. (8)
Theorem (Lapidus, van Frankenhuijsen ’97, ’06, ’13)
For Re(s) > DL we have
ζL(s) =∞∑n=1
mnlsn = s
∫ ∞0
NL(x)x−s−1dx. (9)
John A. Rock (Cal Poly Pomona) A criterion for box-counting measurability June 13th, 2017 13 / 33
Geometric counting functions
Lapidus, van Frankenhuijsen ’97, ’06, ’13For x > 0, the geometric counting function of a fractal string L is given by
NL(x) := #{j ∈ N : `−1j ≤ x} =∑
n∈N, l−1n ≤x
mn. (8)
Theorem (Lapidus, van Frankenhuijsen ’97, ’06, ’13)
For Re(s) > DL we have
ζL(s) =
∞∑n=1
mnlsn = s
∫ ∞0
NL(x)x−s−1dx. (9)
John A. Rock (Cal Poly Pomona) A criterion for box-counting measurability June 13th, 2017 13 / 33
Fractals strings from counting boxes
8
m =
m =
m =
m =1
2
3
4
2
1
4
1
1
2
3
4
Figure: NB(Q, x) where x = ε−1.
Lapidus, R., Zubrinic ’13For A and n ∈ N, let m1 :=M2,mn :=Mn+1 −Mn (n ≥ 2), and
ln := (sup{x ∈ (0,∞) : NB(A, x) =Mn})−1. (10)
John A. Rock (Cal Poly Pomona) A criterion for box-counting measurability June 13th, 2017 14 / 33
Box-counting zeta functions and complex dimensions
Lapidus, R., Zubrinic ’13The box-counting fractal string LB of A is given by
LB := {ln : ln has multiplicity mn, n ∈ N}. (11)
The box-counting zeta function, dimension and complex dimensions of A,denoted ζB, DB, and DB are respectively given by
ζB := ζLB , (12)
DB := DLB , and (13)
DB := DLB . (14)
John A. Rock (Cal Poly Pomona) A criterion for box-counting measurability June 13th, 2017 15 / 33
Box-counting zeta functions and complex dimensions
Lapidus, R., Zubrinic ’13The box-counting fractal string LB of A is given by
LB := {ln : ln has multiplicity mn, n ∈ N}. (11)
The box-counting zeta function, dimension and complex dimensions of A,denoted ζB, DB, and DB are respectively given by
ζB := ζLB , (12)
DB := DLB , and (13)
DB := DLB . (14)
John A. Rock (Cal Poly Pomona) A criterion for box-counting measurability June 13th, 2017 15 / 33
Results from box-counting fractal strings
Proposition (Lapidus, R., Zubrinic ’13)
Let A be an infinite subset of Rm with box-counting fractal string LB andbox-counting function NB(A, x). Then for x ∈ (l−11 ,∞) \ (l−1n )n∈N,
NLB (x) = NB(A, x). (15)
Theorem (Lapidus, R., Zubrinic ’13)
Let A be a bounded infinite subset of Rm. Then
dimBA = DB. (16)
John A. Rock (Cal Poly Pomona) A criterion for box-counting measurability June 13th, 2017 16 / 33
Results from box-counting fractal strings
Proposition (Lapidus, R., Zubrinic ’13)
Let A be an infinite subset of Rm with box-counting fractal string LB andbox-counting function NB(A, x). Then for x ∈ (l−11 ,∞) \ (l−1n )n∈N,
NLB (x) = NB(A, x). (15)
Theorem (Lapidus, R., Zubrinic ’13)
Let A be a bounded infinite subset of Rm. Then
dimBA = DB. (16)
John A. Rock (Cal Poly Pomona) A criterion for box-counting measurability June 13th, 2017 16 / 33
Counting functions over complex dimensions
Theorem (Lapidus, van Frankenhuijsen ’97, ’06, ’13)
Let L be a fractal string such that DL(W ) consists entirely of simplepoles. Then, under certain growth conditions on ζL, we have
NL(x) =∑
ω∈DL(W )
xω
ωres(ζL(s);ω) + {ζL(0)}+R(x), (17)
where R(x) is an error term of small order and the term in braces isincluded only if 0 ∈W\DL.
John A. Rock (Cal Poly Pomona) A criterion for box-counting measurability June 13th, 2017 17 / 33
A criterion for box-counting measurability
Theorem (Giza, Knox, Kurianski, Morales, R. ’17)
Let A ⊆ Rm be a bounded set such that D = dimB A exists. Suppose ζBsatisfies certain growth conditions and has a sufficiently nice meromorphicextension. Then the following are equivalent:
1 D is the only complex dimension with real part D = DB, and it issimple.
2 NB(A, x) = B · xD + o(xD) as x→∞ for some positive constant B.
3 A is box-counting measurable with box-counting content B.
If any of the above conditions holds, then
B = B(A) =res(ζB(A, s);D)
D. (18)
John A. Rock (Cal Poly Pomona) A criterion for box-counting measurability June 13th, 2017 18 / 33
The Riemann zeta function?
Example (Lapidus, R., Zubrinic ’13)
For the unit interval I = [0, 1]× {0}, we have NB(I, x) = dx/2e (theceiling function of x/2). Hence, the box-counting zeta function of I is
ζB(s) =1
2s+
∞∑n=1
1
(2n)s=
1
2s+
1
2sζ(s), (19)
where ζ(s) is the Riemann zeta function.
Example (Dettmers, Giza, Knox, Morales, R. ’17)
Since res(ζ; 1) = 1 and the meromorphic extension of ζ to C does nothave any other pole with real part 1, we have
B(I) = 1/2 = res(ζB; 1)/1. (20)
John A. Rock (Cal Poly Pomona) A criterion for box-counting measurability June 13th, 2017 19 / 33
The Riemann zeta function?
Example (Lapidus, R., Zubrinic ’13)
For the unit interval I = [0, 1]× {0}, we have NB(I, x) = dx/2e (theceiling function of x/2). Hence, the box-counting zeta function of I is
ζB(s) =1
2s+
∞∑n=1
1
(2n)s=
1
2s+
1
2sζ(s), (19)
where ζ(s) is the Riemann zeta function.
Example (Dettmers, Giza, Knox, Morales, R. ’17)
Since res(ζ; 1) = 1 and the meromorphic extension of ζ to C does nothave any other pole with real part 1, we have
B(I) = 1/2 = res(ζB; 1)/1. (20)
John A. Rock (Cal Poly Pomona) A criterion for box-counting measurability June 13th, 2017 19 / 33
Strong separation
1x1x1 4x1/4x1/4 16x1/16x1/16
Let Φ = {ϕj}Nj=1 be a self-similar system with attractor F and scaling
ratios r = (rj)Nj=1. We say F is strongly separated if the ϕj(F ) are
pairwise disjoint and
δ := sup{α : d(x, y) > α, x ∈ ϕj(F ), y ∈ ϕk(F ), j 6= k} (21)
is finite and positive.
John A. Rock (Cal Poly Pomona) A criterion for box-counting measurability June 13th, 2017 20 / 33
Box-counting functions and strong separation
Lemma (Lalley ’88)
Let F ⊆ Rm be a strongly separated self-similar set. Then for any x > 0,
NB(F, x) =N∑j=1
NB(F, rjx) + L(x) (22)
where L(x) is an integer valued step function that vanishes for x > δ−1.
John A. Rock (Cal Poly Pomona) A criterion for box-counting measurability June 13th, 2017 21 / 33
Box-counting zeta functions and strong separation
Theorem (Sargent ’14)
Suppose Φ is a strongly separated self-similar system with attractorF ⊆ Rm and scaling ratios rj , n = 1, . . . , N . Let LB be the box-countingfractal string of F with first length `1. Then
ζB(s) =h(s)
1−∑N
j=1 rsj
(23)
where
h(s) := `s1
N∑j=1
(1− rsj )
+ s
∫ ∞`−11
L(x)x−s−1dx (24)
is an entire function.
John A. Rock (Cal Poly Pomona) A criterion for box-counting measurability June 13th, 2017 22 / 33
ζB and DB of the Quarter Fractal Q
Example (Lapidus, R., Zubrinic ’13; Sargent ’14)
For Q as above we have
ζB(s) =
(√2
2
)s
+
(√2/2)s
+(√
17/8)s
+ (1/2)s
1− 4 · 4−s. (25)
and
DB =
{1 +
2πiz
log 4: z ∈ Z
}. (26)
Q is not box-counting measurable since it has nonreal box-countingcomplex dimensions ω with real part Reω = 1.
John A. Rock (Cal Poly Pomona) A criterion for box-counting measurability June 13th, 2017 23 / 33
ζB and DB of the Quarter Fractal Q
Example (Lapidus, R., Zubrinic ’13; Sargent ’14)
For Q as above we have
ζB(s) =
(√2
2
)s
+
(√2/2)s
+(√
17/8)s
+ (1/2)s
1− 4 · 4−s. (25)
and
DB =
{1 +
2πiz
log 4: z ∈ Z
}. (26)
Q is not box-counting measurable since it has nonreal box-countingcomplex dimensions ω with real part Reω = 1.
John A. Rock (Cal Poly Pomona) A criterion for box-counting measurability June 13th, 2017 23 / 33
ζB and DB of the Quarter Fractal Q
Example (Lapidus, R., Zubrinic ’13; Sargent ’14)
For Q as above we have
ζB(s) =
(√2
2
)s
+
(√2/2)s
+(√
17/8)s
+ (1/2)s
1− 4 · 4−s. (25)
and
DB =
{1 +
2πiz
log 4: z ∈ Z
}. (26)
Q is not box-counting measurable since it has nonreal box-countingcomplex dimensions ω with real part Reω = 1.
John A. Rock (Cal Poly Pomona) A criterion for box-counting measurability June 13th, 2017 23 / 33
Lattice approximation of nonlattice self-similar sets
Theorem (Dettmers, Giza, Knox, Morales, R. ’17)
Suppose Φ is a strongly separated nonlattice self-similar system on Rm
with attractor F , scaling ratios r = (rj)Nj=1, and box-counting complex
dimensions D. Additionally, assume h(s) = 0 if and only if∑N
j=1 rsj = 1.
Then there is a sequence of lattice self-similar systems (ΦM )∞M=1 with,respectively, attractor FM , scaling ratios rM = (rM,j)
Nj=1, and
box-counting complex dimensions DM such that the following hold asM →∞:
rM → r componentwise (via Diophantine approximation);
FM → F in the Hausdorff metric; and
FM is strongly separated for large enough M .
Under additional hypotheses,
DM → D in the sense described in Chapter 3 ofLapidus, van Frankenhuijsen ’97, ’06, ’13.
John A. Rock (Cal Poly Pomona) A criterion for box-counting measurability June 13th, 2017 24 / 33
Lattice approximation of nonlattice self-similar sets
Theorem (Dettmers, Giza, Knox, Morales, R. ’17)
Suppose Φ is a strongly separated nonlattice self-similar system on Rm
with attractor F , scaling ratios r = (rj)Nj=1, and box-counting complex
dimensions D. Additionally, assume h(s) = 0 if and only if∑N
j=1 rsj = 1.
Then there is a sequence of lattice self-similar systems (ΦM )∞M=1 with,respectively, attractor FM , scaling ratios rM = (rM,j)
Nj=1, and
box-counting complex dimensions DM such that the following hold asM →∞:
rM → r componentwise (via Diophantine approximation);
FM → F in the Hausdorff metric; and
FM is strongly separated for large enough M .
Under additional hypotheses,
DM → D in the sense described in Chapter 3 ofLapidus, van Frankenhuijsen ’97, ’06, ’13.
John A. Rock (Cal Poly Pomona) A criterion for box-counting measurability June 13th, 2017 24 / 33
Lattice approximation of nonlattice self-similar sets
Theorem (Dettmers, Giza, Knox, Morales, R. ’17)
Suppose Φ is a strongly separated nonlattice self-similar system on Rm
with attractor F , scaling ratios r = (rj)Nj=1, and box-counting complex
dimensions D. Additionally, assume h(s) = 0 if and only if∑N
j=1 rsj = 1.
Then there is a sequence of lattice self-similar systems (ΦM )∞M=1 with,respectively, attractor FM , scaling ratios rM = (rM,j)
Nj=1, and
box-counting complex dimensions DM such that the following hold asM →∞:
rM → r componentwise (via Diophantine approximation);
FM → F in the Hausdorff metric; and
FM is strongly separated for large enough M .
Under additional hypotheses,
DM → D in the sense described in Chapter 3 ofLapidus, van Frankenhuijsen ’97, ’06, ’13.
John A. Rock (Cal Poly Pomona) A criterion for box-counting measurability June 13th, 2017 24 / 33
Lattice approximation of nonlattice self-similar sets
Theorem (Dettmers, Giza, Knox, Morales, R. ’17)
Suppose Φ is a strongly separated nonlattice self-similar system on Rm
with attractor F , scaling ratios r = (rj)Nj=1, and box-counting complex
dimensions D. Additionally, assume h(s) = 0 if and only if∑N
j=1 rsj = 1.
Then there is a sequence of lattice self-similar systems (ΦM )∞M=1 with,respectively, attractor FM , scaling ratios rM = (rM,j)
Nj=1, and
box-counting complex dimensions DM such that the following hold asM →∞:
rM → r componentwise (via Diophantine approximation);
FM → F in the Hausdorff metric; and
FM is strongly separated for large enough M .
Under additional hypotheses,
DM → D in the sense described in Chapter 3 ofLapidus, van Frankenhuijsen ’97, ’06, ’13.
John A. Rock (Cal Poly Pomona) A criterion for box-counting measurability June 13th, 2017 24 / 33
Lattice approximation of nonlattice self-similar sets
Theorem (Dettmers, Giza, Knox, Morales, R. ’17)
Suppose Φ is a strongly separated nonlattice self-similar system on Rm
with attractor F , scaling ratios r = (rj)Nj=1, and box-counting complex
dimensions D. Additionally, assume h(s) = 0 if and only if∑N
j=1 rsj = 1.
Then there is a sequence of lattice self-similar systems (ΦM )∞M=1 with,respectively, attractor FM , scaling ratios rM = (rM,j)
Nj=1, and
box-counting complex dimensions DM such that the following hold asM →∞:
rM → r componentwise (via Diophantine approximation);
FM → F in the Hausdorff metric; and
FM is strongly separated for large enough M .
Under additional hypotheses,
DM → D in the sense described in Chapter 3 ofLapidus, van Frankenhuijsen ’97, ’06, ’13.
John A. Rock (Cal Poly Pomona) A criterion for box-counting measurability June 13th, 2017 24 / 33
A (generic) nonlattice self-similar set
Figure: Constructing a strongly separated (generic) nonlattice self-similar set Swith scaling ratios 1/2, 1/3, and 1/6.
Let D denote the set of roots of the corresponding Moran equation
3∑j=1
rsj =1
2s+
1
3s+
1
6s= 1. (27)
John A. Rock (Cal Poly Pomona) A criterion for box-counting measurability June 13th, 2017 25 / 33
A (generic) nonlattice self-similar set
Figure: Constructing a strongly separated (generic) nonlattice self-similar set Swith scaling ratios 1/2, 1/3, and 1/6.
Let D denote the set of roots of the corresponding Moran equation
3∑j=1
rsj =1
2s+
1
3s+
1
6s= 1. (27)
John A. Rock (Cal Poly Pomona) A criterion for box-counting measurability June 13th, 2017 25 / 33
A first lattice approximation of D
John A. Rock (Cal Poly Pomona) A criterion for box-counting measurability June 13th, 2017 26 / 33
A second lattice approximation of D
John A. Rock (Cal Poly Pomona) A criterion for box-counting measurability June 13th, 2017 27 / 33
A third lattice approximation of D
John A. Rock (Cal Poly Pomona) A criterion for box-counting measurability June 13th, 2017 28 / 33
A fourth lattice approximation of D
John A. Rock (Cal Poly Pomona) A criterion for box-counting measurability June 13th, 2017 29 / 33
A fifth lattice approximation of D
John A. Rock (Cal Poly Pomona) A criterion for box-counting measurability June 13th, 2017 30 / 33
A sixth lattice approximation of D
John A. Rock (Cal Poly Pomona) A criterion for box-counting measurability June 13th, 2017 31 / 33
A final lattice approximation of D
John A. Rock (Cal Poly Pomona) A criterion for box-counting measurability June 13th, 2017 32 / 33
References
K. Dettmers (now Kurianski), R. Giza, C. Knox, R. Morales, andJ. A. Rock, A survey of complex dimensions, measurability, and thelattice/nonlattice dichotomy, Discrete Contin. Dyn. Syst. Ser. S (2)10 (2017), 213–240.
S. P. Lalley, Packing and covering functions of some self-similarfractals, Indiana Univ. Math. J. 37 (1988), 699–709.
M. L. Lapidus, J. A. Rock, and D. Zubrinic, Box-counting fractalstrings, zeta functions, and equivalent forms of Minkowski dimension,in: Fractal Geometry and Dynamical Systems in Pure and AppliedMathematics, Part 1, Contemporary Mathematics, Amer. Math. Soc.,Providence, RI, 2013.
C. Sargent (now Knox), Box-counting zeta functions of self-similarsets, Master’s thesis, Cal Poly Pomona, 2014.
John A. Rock (Cal Poly Pomona) A criterion for box-counting measurability June 13th, 2017 33 / 33