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Introduction Definition Simulation Parametric models Inference Statistical aspects of determinantal point processes Jesper Møller, Department of Mathematical Sciences, Aalborg University. Joint work with Fr´ ed´ eric Lavancier, Laboratoire de Math´ ematiques Jean Leray, Nantes, and Ege Rubak, Department of Mathematical Sciences, Aalborg University. May 6, 2012

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Page 1: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

Statistical aspects ofdeterminantal point processes

Jesper Møller,Department of Mathematical Sciences, Aalborg University.

Joint work withFrederic Lavancier,

Laboratoire de Mathematiques Jean Leray, Nantes,and

Ege Rubak,

Department of Mathematical Sciences, Aalborg University.

May 6, 2012

Page 2: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

1 Introduction

2 Definition, existence and basic properties

3 Simulation

4 Parametric models

5 Inference

Page 3: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

Introduction

� Determinantal point processes (DPP) form a class ofrepulsive point processes.

� They were introduced in their general form by O. Macchiin 1975 to model fermions (i.e. particules with repulsion) inquantum mechanics.

� Particular cases include the law of the eigenvalues ofcertain random matrices (Gaussian Unitary Ensemble,Ginibre Ensemble,...)

� Most theoretical studies have been published in the 2000’s.

� The statistical aspects have so far been largely unexplored.

Page 4: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

Examples

Poisson DPPDPP with

stronger repulsion

Page 5: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

Statistical motivation

Do DPP’s constitute a tractable and flexible class of models forrepulsive point processes?

−→ Answer: YES.

In fact:

� DPP’s can be easily simulated.

� There are closed form expressions for the moments.

� There is a closed form expression for the density of a DPPon any bounded set.

� Inference is feasible, including likelihood inference.

These properties are unusual for Gibbs point processes whichare commonly used to model inhibition (e.g. the Straussprocess).

Page 6: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

Statistical motivation

Do DPP’s constitute a tractable and flexible class of models forrepulsive point processes?

−→ Answer: YES.

In fact:

� DPP’s can be easily simulated.

� There are closed form expressions for the moments.

� There is a closed form expression for the density of a DPPon any bounded set.

� Inference is feasible, including likelihood inference.

These properties are unusual for Gibbs point processes whichare commonly used to model inhibition (e.g. the Straussprocess).

Page 7: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

Statistical motivation

Do DPP’s constitute a tractable and flexible class of models forrepulsive point processes?

−→ Answer: YES.

In fact:

� DPP’s can be easily simulated.

� There are closed form expressions for the moments.

� There is a closed form expression for the density of a DPPon any bounded set.

� Inference is feasible, including likelihood inference.

These properties are unusual for Gibbs point processes whichare commonly used to model inhibition (e.g. the Straussprocess).

Page 8: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

Statistical motivation

Do DPP’s constitute a tractable and flexible class of models forrepulsive point processes?

−→ Answer: YES.

In fact:

� DPP’s can be easily simulated.

� There are closed form expressions for the moments.

� There is a closed form expression for the density of a DPPon any bounded set.

� Inference is feasible, including likelihood inference.

These properties are unusual for Gibbs point processes whichare commonly used to model inhibition (e.g. the Straussprocess).

Page 9: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

1 Introduction

2 Definition, existence and basic properties

3 Simulation

4 Parametric models

5 Inference

Page 10: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

Notation

� We view a spatial point process X on Rd as a randomlocally finite subset of Rd.

� For any borel set B ⊆ Rd, XB = X ∩B.

� For any integer n > 0, denote ρ(n) the n’th order productdensity function of X.Intuitively,

ρ(n)(x1, . . . , xn) dx1 · · · dxnis the probability that for each i = 1, . . . , n,X has a point in a region around xi of volume dxi.

In particular ρ = ρ(1) is the intensity function.

Page 11: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

Notation

� We view a spatial point process X on Rd as a randomlocally finite subset of Rd.

� For any borel set B ⊆ Rd, XB = X ∩B.

� For any integer n > 0, denote ρ(n) the n’th order productdensity function of X.Intuitively,

ρ(n)(x1, . . . , xn) dx1 · · · dxnis the probability that for each i = 1, . . . , n,X has a point in a region around xi of volume dxi.

In particular ρ = ρ(1) is the intensity function.

Page 12: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

Notation

� We view a spatial point process X on Rd as a randomlocally finite subset of Rd.

� For any borel set B ⊆ Rd, XB = X ∩B.

� For any integer n > 0, denote ρ(n) the n’th order productdensity function of X.Intuitively,

ρ(n)(x1, . . . , xn) dx1 · · · dxnis the probability that for each i = 1, . . . , n,X has a point in a region around xi of volume dxi.

In particular ρ = ρ(1) is the intensity function.

Page 13: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

Notation

� We view a spatial point process X on Rd as a randomlocally finite subset of Rd.

� For any borel set B ⊆ Rd, XB = X ∩B.

� For any integer n > 0, denote ρ(n) the n’th order productdensity function of X.Intuitively,

ρ(n)(x1, . . . , xn) dx1 · · · dxnis the probability that for each i = 1, . . . , n,X has a point in a region around xi of volume dxi.

In particular ρ = ρ(1) is the intensity function.

Page 14: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

Definition of a determinantal point process

For any function C : Rd × Rd → C, denote [C](x1, . . . , xn) then× n matrix with entries C(xi, xj).

Ex.: [C](x1) = C(x1, x1) [C](x1, x2) =

(C(x1, x1) C(x1, x2)C(x2, x1) C(x2, x2)

).

Definition

X is a determinantal point process with kernel C, denotedX ∼ DPP(C), if its product density functions satisfy

ρ(n)(x1, . . . , xn) = det[C](x1, . . . , xn), n = 1, 2, . . .

The Poisson process with intensity ρ(x) is the special casewhere C(x, x) = ρ(x) and C(x, y) = 0 if x 6= y.

For existence, conditions on the kernel C are mandatory,e.g. C must satisfy: for all x1, . . . , xn, det[C](x1, . . . , xn) ≥ 0.

Page 15: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

Definition of a determinantal point process

For any function C : Rd × Rd → C, denote [C](x1, . . . , xn) then× n matrix with entries C(xi, xj).

Ex.: [C](x1) = C(x1, x1) [C](x1, x2) =

(C(x1, x1) C(x1, x2)C(x2, x1) C(x2, x2)

).

Definition

X is a determinantal point process with kernel C, denotedX ∼ DPP(C), if its product density functions satisfy

ρ(n)(x1, . . . , xn) = det[C](x1, . . . , xn), n = 1, 2, . . .

The Poisson process with intensity ρ(x) is the special casewhere C(x, x) = ρ(x) and C(x, y) = 0 if x 6= y.

For existence, conditions on the kernel C are mandatory,e.g. C must satisfy: for all x1, . . . , xn, det[C](x1, . . . , xn) ≥ 0.

Page 16: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

Definition of a determinantal point process

For any function C : Rd × Rd → C, denote [C](x1, . . . , xn) then× n matrix with entries C(xi, xj).

Ex.: [C](x1) = C(x1, x1) [C](x1, x2) =

(C(x1, x1) C(x1, x2)C(x2, x1) C(x2, x2)

).

Definition

X is a determinantal point process with kernel C, denotedX ∼ DPP(C), if its product density functions satisfy

ρ(n)(x1, . . . , xn) = det[C](x1, . . . , xn), n = 1, 2, . . .

The Poisson process with intensity ρ(x) is the special casewhere C(x, x) = ρ(x) and C(x, y) = 0 if x 6= y.

For existence, conditions on the kernel C are mandatory,e.g. C must satisfy: for all x1, . . . , xn, det[C](x1, . . . , xn) ≥ 0.

Page 17: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

Definition of a determinantal point process

For any function C : Rd × Rd → C, denote [C](x1, . . . , xn) then× n matrix with entries C(xi, xj).

Ex.: [C](x1) = C(x1, x1) [C](x1, x2) =

(C(x1, x1) C(x1, x2)C(x2, x1) C(x2, x2)

).

Definition

X is a determinantal point process with kernel C, denotedX ∼ DPP(C), if its product density functions satisfy

ρ(n)(x1, . . . , xn) = det[C](x1, . . . , xn), n = 1, 2, . . .

The Poisson process with intensity ρ(x) is the special casewhere C(x, x) = ρ(x) and C(x, y) = 0 if x 6= y.

For existence, conditions on the kernel C are mandatory,e.g. C must satisfy: for all x1, . . . , xn, det[C](x1, . . . , xn) ≥ 0.

Page 18: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

First properties

� From the definition, if C is continuous,

ρ(n)(x1, . . . , xn) ≈ 0 whenever xi ≈ xj for some i 6= j,

=⇒ the points of X repel each other.

� The intensity of X is ρ(x) = C(x, x).

� The pair correlation function is

g(x, y) :=ρ(2)(x, y)

ρ(x)ρ(y)= 1− C(x, y)C(y, x)

C(x, x)C(y, y)

� Thus g ≤ 1 (i.e. repulsiveness).

� If X ∼ DPP(C), then XB ∼ DPPB(CB)

� Any smooth transformation or independent thinning of aDPP is still a DPP with explicit given kernel.

� There exists at most one DPP(C).

Page 19: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

First properties

� From the definition, if C is continuous,

ρ(n)(x1, . . . , xn) ≈ 0 whenever xi ≈ xj for some i 6= j,

=⇒ the points of X repel each other.

� The intensity of X is ρ(x) = C(x, x).

� The pair correlation function is

g(x, y) :=ρ(2)(x, y)

ρ(x)ρ(y)= 1− C(x, y)C(y, x)

C(x, x)C(y, y)

� Thus g ≤ 1 (i.e. repulsiveness).

� If X ∼ DPP(C), then XB ∼ DPPB(CB)

� Any smooth transformation or independent thinning of aDPP is still a DPP with explicit given kernel.

� There exists at most one DPP(C).

Page 20: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

First properties

� From the definition, if C is continuous,

ρ(n)(x1, . . . , xn) ≈ 0 whenever xi ≈ xj for some i 6= j,

=⇒ the points of X repel each other.

� The intensity of X is ρ(x) = C(x, x).

� The pair correlation function is

g(x, y) :=ρ(2)(x, y)

ρ(x)ρ(y)= 1− C(x, y)C(y, x)

C(x, x)C(y, y)

� Thus g ≤ 1 (i.e. repulsiveness).

� If X ∼ DPP(C), then XB ∼ DPPB(CB)

� Any smooth transformation or independent thinning of aDPP is still a DPP with explicit given kernel.

� There exists at most one DPP(C).

Page 21: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

First properties

� From the definition, if C is continuous,

ρ(n)(x1, . . . , xn) ≈ 0 whenever xi ≈ xj for some i 6= j,

=⇒ the points of X repel each other.

� The intensity of X is ρ(x) = C(x, x).

� The pair correlation function is

g(x, y) :=ρ(2)(x, y)

ρ(x)ρ(y)= 1− C(x, y)C(y, x)

C(x, x)C(y, y)

� Thus g ≤ 1 (i.e. repulsiveness).

� If X ∼ DPP(C), then XB ∼ DPPB(CB)

� Any smooth transformation or independent thinning of aDPP is still a DPP with explicit given kernel.

� There exists at most one DPP(C).

Page 22: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

First properties

� From the definition, if C is continuous,

ρ(n)(x1, . . . , xn) ≈ 0 whenever xi ≈ xj for some i 6= j,

=⇒ the points of X repel each other.

� The intensity of X is ρ(x) = C(x, x).

� The pair correlation function is

g(x, y) :=ρ(2)(x, y)

ρ(x)ρ(y)= 1− C(x, y)C(y, x)

C(x, x)C(y, y)

� Thus g ≤ 1 (i.e. repulsiveness).

� If X ∼ DPP(C), then XB ∼ DPPB(CB)

� Any smooth transformation or independent thinning of aDPP is still a DPP with explicit given kernel.

� There exists at most one DPP(C).

Page 23: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

First properties

� From the definition, if C is continuous,

ρ(n)(x1, . . . , xn) ≈ 0 whenever xi ≈ xj for some i 6= j,

=⇒ the points of X repel each other.

� The intensity of X is ρ(x) = C(x, x).

� The pair correlation function is

g(x, y) :=ρ(2)(x, y)

ρ(x)ρ(y)= 1− C(x, y)C(y, x)

C(x, x)C(y, y)

� Thus g ≤ 1 (i.e. repulsiveness).

� If X ∼ DPP(C), then XB ∼ DPPB(CB)

� Any smooth transformation or independent thinning of aDPP is still a DPP with explicit given kernel.

� There exists at most one DPP(C).

Page 24: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

Existence

In all that follows we assume

(C1) C is a continuous complex covariance function.

By Mercer’s theorem, for any compact set S ⊂ Rd, C restrictedto S × S, denoted CS , has a spectral representation,

CS(x, y) =∞∑k=1

λSkφSk (x)φSk (y), (x, y) ∈ S × S,

where λSk ≥ 0 and∫S φ

Sk (x)φSl (x) dx = 1{k=l}.

Theorem (Macchi, 1975; Hough et al., 2009; our paper)

Under (C1), existence of DPP(C) is equivalent to that

λSk ≤ 1 for all compact S ⊂ Rd and all k.

Page 25: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

Existence

In all that follows we assume

(C1) C is a continuous complex covariance function.

By Mercer’s theorem, for any compact set S ⊂ Rd, C restrictedto S × S, denoted CS , has a spectral representation,

CS(x, y) =

∞∑k=1

λSkφSk (x)φSk (y), (x, y) ∈ S × S,

where λSk ≥ 0 and∫S φ

Sk (x)φSl (x) dx = 1{k=l}.

Theorem (Macchi, 1975; Hough et al., 2009; our paper)

Under (C1), existence of DPP(C) is equivalent to that

λSk ≤ 1 for all compact S ⊂ Rd and all k.

Page 26: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

Existence

In all that follows we assume

(C1) C is a continuous complex covariance function.

By Mercer’s theorem, for any compact set S ⊂ Rd, C restrictedto S × S, denoted CS , has a spectral representation,

CS(x, y) =

∞∑k=1

λSkφSk (x)φSk (y), (x, y) ∈ S × S,

where λSk ≥ 0 and∫S φ

Sk (x)φSl (x) dx = 1{k=l}.

Theorem (Macchi, 1975; Hough et al., 2009; our paper)

Under (C1), existence of DPP(C) is equivalent to that

λSk ≤ 1 for all compact S ⊂ Rd and all k.

Page 27: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

Density on a compact set S

Let XS ∼ DPPS(CS) with S ⊂ Rd compact.

Recall that CS(x, y) =∑∞

k=1 λSkφ

Sk (x)φSk (y).

Theorem (Macchi, 1975)

Assuming λSk < 1, for all k, then XS is absolutely continuouswith respect to the homogeneous Poisson process on S with unitintensity, and has density

f({x1, . . . , xn}) = exp(|S| −D) det[C](x1, . . . , xn),

where D = −∑∞

k=1 log(1− λSk ) and C : S × S → C is given by

C(x, y) =∞∑k=1

λSk1− λSk

φSk (x)φSk (y)

Page 28: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

Density on a compact set S

Let XS ∼ DPPS(CS) with S ⊂ Rd compact.

Recall that CS(x, y) =∑∞

k=1 λSkφ

Sk (x)φSk (y).

Theorem (Macchi, 1975)

Assuming λSk < 1, for all k, then XS is absolutely continuouswith respect to the homogeneous Poisson process on S with unitintensity, and has density

f({x1, . . . , xn}) = exp(|S| −D) det[C](x1, . . . , xn),

where D = −∑∞

k=1 log(1− λSk ) and C : S × S → C is given by

C(x, y) =

∞∑k=1

λSk1− λSk

φSk (x)φSk (y)

Page 29: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

1 Introduction

2 Definition, existence and basic properties

3 Simulation

4 Parametric models

5 Inference

Page 30: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

Let XS ∼ DPPS(CS) where S ⊂ Rd is compact.

We want to simulate XS .

Recall that CS(x, y) =∑∞

k=1 λSkφ

Sk (x)φSk (y).

Theorem (Hough et al., 2006)

For k ∈ N, let Bk be independent Bernoulli r.v.’s with meansλSk . Define

K(x, y) =∞∑k=1

BkφSk (x)φSk (y), (x, y) ∈ S × S.

Then DPPS(CS)d= DPPS(K).

Page 31: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

Let XS ∼ DPPS(CS) where S ⊂ Rd is compact.

We want to simulate XS .

Recall that CS(x, y) =∑∞

k=1 λSkφ

Sk (x)φSk (y).

Theorem (Hough et al., 2006)

For k ∈ N, let Bk be independent Bernoulli r.v.’s with meansλSk . Define

K(x, y) =∞∑k=1

BkφSk (x)φSk (y), (x, y) ∈ S × S.

Then DPPS(CS)d= DPPS(K).

Page 32: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

So simulating XS is equivalent to simulate DPPS(K) with

K(x, y) =

∞∑k=1

BkφSk (x)φSk (y), (x, y) ∈ S × S.

Let M = max{k ≥ 0;Bk 6= 0}.Note that M is a.s. finite, since

∑λSk =

∫S C(x, x) dx <∞.

1 simulate a realization M = m (by the inversion method);

2 generate the Bernoulli variables B1, . . . , Bm−1 (these areindependent of {M = n});

3 simulate the point process DPPS(K) given B1, . . . , BM andM = m.

In step 3, the kernel K becomes a projection kernel, and w.l.o.g.

K(x, y) =n∑k=1

φSk (x)φSk (y)

where n = #{1 ≤ k ≤M : Bk = 1}.

Page 33: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

So simulating XS is equivalent to simulate DPPS(K) with

K(x, y) =

∞∑k=1

BkφSk (x)φSk (y), (x, y) ∈ S × S.

Let M = max{k ≥ 0;Bk 6= 0}.Note that M is a.s. finite, since

∑λSk =

∫S C(x, x) dx <∞.

1 simulate a realization M = m (by the inversion method);

2 generate the Bernoulli variables B1, . . . , Bm−1 (these areindependent of {M = n});

3 simulate the point process DPPS(K) given B1, . . . , BM andM = m.

In step 3, the kernel K becomes a projection kernel, and w.l.o.g.

K(x, y) =n∑k=1

φSk (x)φSk (y)

where n = #{1 ≤ k ≤M : Bk = 1}.

Page 34: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

So simulating XS is equivalent to simulate DPPS(K) with

K(x, y) =

∞∑k=1

BkφSk (x)φSk (y), (x, y) ∈ S × S.

Let M = max{k ≥ 0;Bk 6= 0}.Note that M is a.s. finite, since

∑λSk =

∫S C(x, x) dx <∞.

1 simulate a realization M = m (by the inversion method);

2 generate the Bernoulli variables B1, . . . , Bm−1 (these areindependent of {M = n});

3 simulate the point process DPPS(K) given B1, . . . , BM andM = m.

In step 3, the kernel K becomes a projection kernel, and w.l.o.g.

K(x, y) =n∑k=1

φSk (x)φSk (y)

where n = #{1 ≤ k ≤M : Bk = 1}.

Page 35: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

So simulating XS is equivalent to simulate DPPS(K) with

K(x, y) =

∞∑k=1

BkφSk (x)φSk (y), (x, y) ∈ S × S.

Let M = max{k ≥ 0;Bk 6= 0}.Note that M is a.s. finite, since

∑λSk =

∫S C(x, x) dx <∞.

1 simulate a realization M = m (by the inversion method);

2 generate the Bernoulli variables B1, . . . , Bm−1 (these areindependent of {M = n});

3 simulate the point process DPPS(K) given B1, . . . , BM andM = m.

In step 3, the kernel K becomes a projection kernel, and w.l.o.g.

K(x, y) =n∑k=1

φSk (x)φSk (y)

where n = #{1 ≤ k ≤M : Bk = 1}.

Page 36: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

So simulating XS is equivalent to simulate DPPS(K) with

K(x, y) =

∞∑k=1

BkφSk (x)φSk (y), (x, y) ∈ S × S.

Let M = max{k ≥ 0;Bk 6= 0}.Note that M is a.s. finite, since

∑λSk =

∫S C(x, x) dx <∞.

1 simulate a realization M = m (by the inversion method);

2 generate the Bernoulli variables B1, . . . , Bm−1 (these areindependent of {M = n});

3 simulate the point process DPPS(K) given B1, . . . , BM andM = m.

In step 3, the kernel K becomes a projection kernel, and w.l.o.g.

K(x, y) =n∑k=1

φSk (x)φSk (y)

where n = #{1 ≤ k ≤M : Bk = 1}.

Page 37: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

So simulating XS is equivalent to simulate DPPS(K) with

K(x, y) =

∞∑k=1

BkφSk (x)φSk (y), (x, y) ∈ S × S.

Let M = max{k ≥ 0;Bk 6= 0}.Note that M is a.s. finite, since

∑λSk =

∫S C(x, x) dx <∞.

1 simulate a realization M = m (by the inversion method);

2 generate the Bernoulli variables B1, . . . , Bm−1 (these areindependent of {M = n});

3 simulate the point process DPPS(K) given B1, . . . , BM andM = m.

In step 3, the kernel K becomes a projection kernel, and w.l.o.g.

K(x, y) =

n∑k=1

φSk (x)φSk (y)

where n = #{1 ≤ k ≤M : Bk = 1}.

Page 38: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

Simulation of determinantal projection processes

Denoting v(x) = (φS1 (x), . . . , φSn(x))T , we have

K(x, y) =

n∑k=1

φSk (x)φSk (y) = v(y)∗v(x)

The point process DPPS(K) has a.s. n points (X1, . . . , Xn) that canbe simulated by the following Gram-Schmidt procedure:

sample Xn from the distribution with density pn(x) = ‖v(x)‖2/n.set e1 = v(Xn)/‖v(Xn)‖.for i = (n− 1) to 1 do

sample Xi from the distribution (given Xi+1, . . . , Xn) :

pi(x) =1

i

‖v(x)‖2 −n−i∑j=1

|e∗jv(x)|2 , x ∈ S

set wi = v(Xi)−∑n−ij=1

(e∗jv(Xi)

)ej , en−i+1 = wi/‖wi‖

Theorem

{X1, . . . , Xn} generated as above has distribution DPPS(K).

Page 39: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

Simulation of determinantal projection processes

Denoting v(x) = (φS1 (x), . . . , φSn(x))T , we have

K(x, y) =

n∑k=1

φSk (x)φSk (y) = v(y)∗v(x)

The point process DPPS(K) has a.s. n points (X1, . . . , Xn) that canbe simulated by the following Gram-Schmidt procedure:

sample Xn from the distribution with density pn(x) = ‖v(x)‖2/n.set e1 = v(Xn)/‖v(Xn)‖.for i = (n− 1) to 1 do

sample Xi from the distribution (given Xi+1, . . . , Xn) :

pi(x) =1

i

‖v(x)‖2 −n−i∑j=1

|e∗jv(x)|2 , x ∈ S

set wi = v(Xi)−∑n−ij=1

(e∗jv(Xi)

)ej , en−i+1 = wi/‖wi‖

Theorem

{X1, . . . , Xn} generated as above has distribution DPPS(K).

Page 40: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

Simulation of determinantal projection processes

Denoting v(x) = (φS1 (x), . . . , φSn(x))T , we have

K(x, y) =

n∑k=1

φSk (x)φSk (y) = v(y)∗v(x)

The point process DPPS(K) has a.s. n points (X1, . . . , Xn) that canbe simulated by the following Gram-Schmidt procedure:

sample Xn from the distribution with density pn(x) = ‖v(x)‖2/n.set e1 = v(Xn)/‖v(Xn)‖.for i = (n− 1) to 1 do

sample Xi from the distribution (given Xi+1, . . . , Xn) :

pi(x) =1

i

‖v(x)‖2 −n−i∑j=1

|e∗jv(x)|2 , x ∈ S

set wi = v(Xi)−∑n−ij=1

(e∗jv(Xi)

)ej , en−i+1 = wi/‖wi‖

Theorem

{X1, . . . , Xn} generated as above has distribution DPPS(K).

Page 41: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

Simulation of determinantal projection processes

Denoting v(x) = (φS1 (x), . . . , φSn(x))T , we have

K(x, y) =

n∑k=1

φSk (x)φSk (y) = v(y)∗v(x)

The point process DPPS(K) has a.s. n points (X1, . . . , Xn) that canbe simulated by the following Gram-Schmidt procedure:

sample Xn from the distribution with density pn(x) = ‖v(x)‖2/n.set e1 = v(Xn)/‖v(Xn)‖.for i = (n− 1) to 1 do

sample Xi from the distribution (given Xi+1, . . . , Xn) :

pi(x) =1

i

‖v(x)‖2 −n−i∑j=1

|e∗jv(x)|2 , x ∈ S

set wi = v(Xi)−∑n−ij=1

(e∗jv(Xi)

)ej , en−i+1 = wi/‖wi‖

Theorem

{X1, . . . , Xn} generated as above has distribution DPPS(K).

Page 42: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

Illustration of simulation algorithm

Example: Let S = [−1/2, 1/2]2 and

φk(x) = e2πik·x, k ∈ Z2, x ∈ S,

for a set of indices k1, . . . , kn in Z2.So the projection kernel writes

K(x, y) =

n∑j=1

e2πikj ·(x−y)

and XS ∼ DPPS(K) is homogeneous and has a.s. n points.

Page 43: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

Illustration of simulation algorithm

Step 1. The first point is sampled uniformly on S

Page 44: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

Illustration of simulation algorithm

Step 1. The first point is sampled uniformly on SStep 2. The next point is sampled w.r.t. the following density :

00.

20.

40.

60.

81

Page 45: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

Illustration of simulation algorithm

Step 3. The next point is sampled w.r.t. the following density :

00.

20.

40.

60.

81

Page 46: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

Illustration of simulation algorithm

etc.

00.

20.

40.

60.

81

Page 47: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

Illustration of simulation algorithm

etc.

00.

20.

40.

60.

81

Page 48: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

Illustration of simulation algorithm

etc.

00.

10.

20.

30.

40.

50.

6

● ●

● ●

Page 49: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

Illustration of simulation algorithm

etc.

00.

050.

10.

15

● ●

● ●

● ●●

Page 50: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

1 Introduction

2 Definition, existence and basic properties

3 Simulation

4 Parametric models

5 Inference

Page 51: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

Stationary models

We focus on a kernel C of the form

C(x, y) = C0(x− y), x, y ∈ Rd.

(C1) C0 is a continuous covariance functionMoreover, if C0 ∈ L2(Rd) we can define its Fourier transform

ϕ(x) =

∫C0(t)e−2πix·t dt, x ∈ Rd.

Theorem

Under (C1), if C0 ∈ L2(Rd), then existence of DPP(C0) isequivalent to

ϕ ≤ 1.

To construct parametric families of DPP :Consider parametric families of C0 and rescale so that ϕ ≤ 1.→ This will induce a bound on the parameter space.

Page 52: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

Stationary models

We focus on a kernel C of the form

C(x, y) = C0(x− y), x, y ∈ Rd.

(C1) C0 is a continuous covariance functionMoreover, if C0 ∈ L2(Rd) we can define its Fourier transform

ϕ(x) =

∫C0(t)e−2πix·t dt, x ∈ Rd.

Theorem

Under (C1), if C0 ∈ L2(Rd), then existence of DPP(C0) isequivalent to

ϕ ≤ 1.

To construct parametric families of DPP :Consider parametric families of C0 and rescale so that ϕ ≤ 1.→ This will induce a bound on the parameter space.

Page 53: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

Stationary models

We focus on a kernel C of the form

C(x, y) = C0(x− y), x, y ∈ Rd.

(C1) C0 is a continuous covariance functionMoreover, if C0 ∈ L2(Rd) we can define its Fourier transform

ϕ(x) =

∫C0(t)e−2πix·t dt, x ∈ Rd.

Theorem

Under (C1), if C0 ∈ L2(Rd), then existence of DPP(C0) isequivalent to

ϕ ≤ 1.

To construct parametric families of DPP :Consider parametric families of C0 and rescale so that ϕ ≤ 1.→ This will induce a bound on the parameter space.

Page 54: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

Several parametric families of covariance function are available, withclosed form expressions for their Fourier transform.

� For d = 2, the circular covariance function with range α is given by

C0(x) = ρ2

π

(arccos(‖x‖/α)− ‖x‖/α

√1− (‖x‖/α)2

)1‖x‖<α.

DPP(C0) exists iff ϕ ≤ 1⇔ ρα2 ≤ 4/π.

⇒ Tradeoff between the intensity ρ and the range of repulsion α.

� Whittle-Matern (includes Exponential and Gaussian) :

C0(x) = ρ21−ν

Γ(ν)‖x/α‖νKν(‖x/α‖), x ∈ Rd.

DPP(C0) exists iff ρ ≤ Γ(ν)Γ(ν+d/2)(2

√πα)d

.

� Generalized Cauchy

C0(x) =ρ

(1 + ‖x/α‖2)ν+d/2

, x ∈ Rd.

DPP(C0) exists iff ρ ≤ Γ(ν+d/2)Γ(ν)(

√πα)d

.

Page 55: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

Several parametric families of covariance function are available, withclosed form expressions for their Fourier transform.

� For d = 2, the circular covariance function with range α is given by

C0(x) = ρ2

π

(arccos(‖x‖/α)− ‖x‖/α

√1− (‖x‖/α)2

)1‖x‖<α.

DPP(C0) exists iff ϕ ≤ 1⇔ ρα2 ≤ 4/π.

⇒ Tradeoff between the intensity ρ and the range of repulsion α.

� Whittle-Matern (includes Exponential and Gaussian) :

C0(x) = ρ21−ν

Γ(ν)‖x/α‖νKν(‖x/α‖), x ∈ Rd.

DPP(C0) exists iff ρ ≤ Γ(ν)Γ(ν+d/2)(2

√πα)d

.

� Generalized Cauchy

C0(x) =ρ

(1 + ‖x/α‖2)ν+d/2

, x ∈ Rd.

DPP(C0) exists iff ρ ≤ Γ(ν+d/2)Γ(ν)(

√πα)d

.

Page 56: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

Several parametric families of covariance function are available, withclosed form expressions for their Fourier transform.

� For d = 2, the circular covariance function with range α is given by

C0(x) = ρ2

π

(arccos(‖x‖/α)− ‖x‖/α

√1− (‖x‖/α)2

)1‖x‖<α.

DPP(C0) exists iff ϕ ≤ 1⇔ ρα2 ≤ 4/π.

⇒ Tradeoff between the intensity ρ and the range of repulsion α.

� Whittle-Matern (includes Exponential and Gaussian) :

C0(x) = ρ21−ν

Γ(ν)‖x/α‖νKν(‖x/α‖), x ∈ Rd.

DPP(C0) exists iff ρ ≤ Γ(ν)Γ(ν+d/2)(2

√πα)d

.

� Generalized Cauchy

C0(x) =ρ

(1 + ‖x/α‖2)ν+d/2

, x ∈ Rd.

DPP(C0) exists iff ρ ≤ Γ(ν+d/2)Γ(ν)(

√πα)d

.

Page 57: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

Pair correlation functions of DPP(C0) for previous models :

In blue : C0 is the circular covariance function.

In red : C0 is Whittle-Matern, for different values of ν

In green : C0 is generalized Cauchy, for different values of ν

The parameter α is chosen such that the range of corr. ≈ 1.

0.0 0.2 0.4 0.6 0.8 1.0

0.0

0.2

0.4

0.6

0.8

1.0

r = |x − y|

g(r)

Page 58: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

Spectral approach

� Specify a parametric class of integrable functionsϕθ : Rd → [0, 1] (spectral densities).

� This is all we need for having a well-defined DDP.

� Is convenient for simulation and for (approximate) densitycalculations as seen later.

� Example: power exponential spectral model:

ϕρ,ν,α(x) = ρΓ(d/2 + 1)ναd

dπd/2Γ(d/ν)exp (−‖αx‖ν)

with

ρ > 0, ν > 0, 0 < α < αmax(ρ, ν) :=

(2πd/2Γ(d/ν + 1)

ρΓ(d/2)

)1/d

.

Page 59: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

Spectral approach

� Specify a parametric class of integrable functionsϕθ : Rd → [0, 1] (spectral densities).

� This is all we need for having a well-defined DDP.

� Is convenient for simulation and for (approximate) densitycalculations as seen later.

� Example: power exponential spectral model:

ϕρ,ν,α(x) = ρΓ(d/2 + 1)ναd

dπd/2Γ(d/ν)exp (−‖αx‖ν)

with

ρ > 0, ν > 0, 0 < α < αmax(ρ, ν) :=

(2πd/2Γ(d/ν + 1)

ρΓ(d/2)

)1/d

.

Page 60: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

Power exponential spectral model: (isotropic) spectraldensities and pair correlation functions

0 5 10 15

0.0

0.2

0.4

0.6

0.8

1.0

ν = 1ν = 2 (Gauss)ν = 3ν = 5ν = 10ν = ∞

0.00 0.05 0.10 0.15 0.20

0.0

0.2

0.4

0.6

0.8

1.0

ν = 1ν = 2 (Gauss)ν = 3ν = 5ν = 10ν = ∞

Spectral densities Pair correlation functions

Page 61: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

Approximation of stationary models

Consider a stationary kernel C0 and X ∼ DPP(C0).• The simulation and the density of XS requires the expansion

CS(x, y) = C0(y − x) =

∞∑k=1

λSkφSk (x)φSk (y), (x, y) ∈ S × S,

but in general λSk and φSk are not expressible on closed form.

• Consider the unit box S = [− 12 ,

12 ]d and the Fourier expansion

C0(y − x) =∑k∈Zd

cke2πik·(y−x), y − x ∈ S.

The Fourier coefficients are

ck =

∫S

C0(u)e−2πik·u du ≈∫Rd

C0(u)e−2πik·u du = ϕ(k)

which is a good approximation if C0(u) ≈ 0 for |u| > 12 .

• Example: For the circular covariance, this is true whenever ρ > 5.

Page 62: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

Approximation of stationary models

Consider a stationary kernel C0 and X ∼ DPP(C0).• The simulation and the density of XS requires the expansion

CS(x, y) = C0(y − x) =

∞∑k=1

λSkφSk (x)φSk (y), (x, y) ∈ S × S,

but in general λSk and φSk are not expressible on closed form.• Consider the unit box S = [− 1

2 ,12 ]d and the Fourier expansion

C0(y − x) =∑k∈Zd

cke2πik·(y−x), y − x ∈ S.

The Fourier coefficients are

ck =

∫S

C0(u)e−2πik·u du ≈∫Rd

C0(u)e−2πik·u du = ϕ(k)

which is a good approximation if C0(u) ≈ 0 for |u| > 12 .

• Example: For the circular covariance, this is true whenever ρ > 5.

Page 63: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

Approximation of stationary models

Consider a stationary kernel C0 and X ∼ DPP(C0).• The simulation and the density of XS requires the expansion

CS(x, y) = C0(y − x) =

∞∑k=1

λSkφSk (x)φSk (y), (x, y) ∈ S × S,

but in general λSk and φSk are not expressible on closed form.• Consider the unit box S = [− 1

2 ,12 ]d and the Fourier expansion

C0(y − x) =∑k∈Zd

cke2πik·(y−x), y − x ∈ S.

The Fourier coefficients are

ck =

∫S

C0(u)e−2πik·u du ≈∫Rd

C0(u)e−2πik·u du = ϕ(k)

which is a good approximation if C0(u) ≈ 0 for |u| > 12 .

• Example: For the circular covariance, this is true whenever ρ > 5.

Page 64: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

Approximation of stationary models

The approximation of DPP(C0) on S is then DPPS(Capp,0) with

Capp,0(x− y) =∑k∈Zd

ϕ(k)e2πi(x−y)·k, x, y ∈ S,

where ϕ is the Fourier transform of C0.

This approximation allows us

� to simulate DPP(C0) on S;

� to compute the (approximated) density of DPP(C0) on S.

Page 65: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

Approximation of stationary models

The approximation of DPP(C0) on S is then DPPS(Capp,0) with

Capp,0(x− y) =∑k∈Zd

ϕ(k)e2πi(x−y)·k, x, y ∈ S,

where ϕ is the Fourier transform of C0.

This approximation allows us

� to simulate DPP(C0) on S;

� to compute the (approximated) density of DPP(C0) on S.

Page 66: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

1 Introduction

2 Definition, existence and basic properties

3 Simulation

4 Parametric models

5 Inference

Page 67: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

Consider a stationary and isotropic parametric DPP(C), i.e.

C(x, y) = C0(x− y) = ρRα(‖x− y‖),

with Rα(0) = 1.

The first and second moments are easily deduced:

� The intensity is ρ.

� The pair correlation function is

g(x, y) = g0(‖x− y‖) = 1−R2α(‖x− y‖).

� Ripley’s K-function is easily expressible in terms of Rα: ifd = 2,

Kα(r) := 2π

∫ r

0tg0(t) dt = πr2 − 2π

∫ r

0t|Rα(t)|2 dt.

Page 68: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

Inference

Parameter estimation can be conducted as follows.

1 Estimate ρ by #{obs. points}/area of obs. window.2 Estimate α

either by minimum contrast estimator (MCE):

α = argminα

∫ rmax

0

∣∣∣∣√K(r)−√Kα(r)

∣∣∣∣2 dr

or by maximum likelihood estimator: given ρ, thelikelihood is deduced from the kernel approximation.

Page 69: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

Two model examples

� Exponential model with ρ = 200and α = 0.014:

C0(x) = ρ exp(−‖x‖/α).

� Gaussian model withρ = 200 and α = 0.02:

C0(x) = ρ exp(−‖x/α‖2).0.00 0.02 0.04 0.06 0.08 0.10

0.0

0.2

0.4

0.6

0.8

1.0

●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●

●●●●●

●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●

Exponential modelGaussian model

− Solid lines: theoretical pair correlation function

◦ Circles: pair correlation from the approximated kernel

Page 70: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

Samples from the Gaussian model on [0, 1]2:

● ●

●●

●●

●●

●●

●●

● ●

●●

●●

●●

●●

●●

●●

●●

●●

● ●

● ●

●●

● ●●

● ●●

● ●●

●●

●●

●●

●●

●●

●●

●●

●●

●●

●●

●●

●●

●●

●●

Samples from the exponential model on [0, 1]2:

●●

●●

●●

● ●

●●

●●

●●

●●

●●

●●

●●

●●

●●

●●

●●

●●

●●

● ●

●●

●●

●●

●●

● ●

●●

●●

●●

●●

●●

● ●

●●

●●

● ●

Page 71: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

Estimation of α from 200 realisations

MCE MLE

0.00

50.

015

0.02

50.

035

MCE MLE0.

000

0.01

00.

020

0.03

0

Gaussian model Exponential model

Page 72: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

Example: 134 Norwegian pine trees observed in a56× 38 m region

●●

●●

● ●

● ●

● ●

●●

●●

●●

● ●

●●

●●

●●

●●

●●

●●

● ●

●●

Møller and Waagpetersen (2004): a five parameter multiscaleprocess is fitted using elaborate MCMC MLE methods.

Here we fit a more parsimonious DPP models.

Page 73: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

First,

� Whittle-Matern model;

� Cauchy model;

� Gaussian model: the best fit, but plots of summarystatistics indicate a lack of fit.

Second,

� power exponential spectral model: provides a much betterfit, with

ν = 10, α = 6.36 ≈ αmax = 6.77

i.e. close to the “most repulsive possible stationary DPP”.

Page 74: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

First,

� Whittle-Matern model;

� Cauchy model;

� Gaussian model: the best fit, but plots of summarystatistics indicate a lack of fit.

Second,

� power exponential spectral model: provides a much betterfit, with

ν = 10, α = 6.36 ≈ αmax = 6.77

i.e. close to the “most repulsive possible stationary DPP”.

Page 75: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

0 2 4 6 8

−1.

2−

0.8

−0.

40.

0

GaussPower exp.Data

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

0.0

0.2

0.4

0.6

0.8

GaussPower exp.Data

0.0 0.5 1.0 1.5 2.0 2.5

0.0

0.2

0.4

0.6

0.8 Gauss

Power exp.Data

0.0 0.5 1.0 1.5 2.0 2.5

12

34

GaussPower exp.Data

Clockwise from topleft: L(r)− r; G(r); F (r); J(r). Simulated 2.5% and 97.5%envelopes are based on 4000 realizations of the fitted Gaussianmodel resp. power exponential spectral model.

Page 76: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

Conclusions

• DPP’s provide flexible parametric models of repulsive pointprocesses.

• DPP’s possess the following appealing properties:

� Easily simulated.

� Closed form expressions for the moments.

� Closed form expression for the density of a DPP on anybounded set.

� Inference is feasible, including likelihood inference.

⇒ Promising alternative to repulsive Gibbs point processes.

Page 77: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

Conclusions

• DPP’s provide flexible parametric models of repulsive pointprocesses.

• DPP’s possess the following appealing properties:

� Easily simulated.

� Closed form expressions for the moments.

� Closed form expression for the density of a DPP on anybounded set.

� Inference is feasible, including likelihood inference.

⇒ Promising alternative to repulsive Gibbs point processes.

Page 78: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

Conclusions

• DPP’s provide flexible parametric models of repulsive pointprocesses.

• DPP’s possess the following appealing properties:

� Easily simulated.

� Closed form expressions for the moments.

� Closed form expression for the density of a DPP on anybounded set.

� Inference is feasible, including likelihood inference.

⇒ Promising alternative to repulsive Gibbs point processes.

Page 79: Statistical aspects of determinantal point processes · Statistical aspects of determinantal point processes Jesper M˝ller, Department of Mathematical Sciences, Aalborg University

Introduction Definition Simulation Parametric models Inference

References

Hough, J. B., M. Krishnapur, Y. Peres, and B. Virag (2006).Determinantal processes and independence.Probability Surveys 3, 206–229.

Macchi, O. (1975).The coincidence approach to stochastic point processes.Advances in Applied Probability 7, 83–122.

McCullagh, P. and J. Møller (2006).The permanental process.Advances in Applied Probability 38, 873–888.

Scardicchio, A., C. Zachary, and S. Torquato (2009).Statistical properties of determinantal point processes in high-dimensionalEuclidean spaces.Physical Review E 79 (4).

Shirai, T. and Y. Takahashi (2003).Random point fields associated with certain Fredholm determinants. I.Fermion, Poisson and boson point processes.Journal of Functional Analysis 2, 414–463.

Soshnikov, A. (2000).Determinantal random point fields.Russian Math. Surveys 55, 923–975.