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HAL Id: hal-01030745 https://hal.inria.fr/hal-01030745 Submitted on 22 Jul 2014 HAL is a multi-disciplinary open access archive for the deposit and dissemination of sci- entific research documents, whether they are pub- lished or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés. (Un)conditional consensus emergence under perturbed and decentralized feedback controls Mattia Bongini, Dante Kalise, Massimo Fornasier To cite this version: Mattia Bongini, Dante Kalise, Massimo Fornasier. (Un)conditional consensus emergence under per- turbed and decentralized feedback controls. NETCO 2014 - New Trends in Optimal Control, Jun 2014, Tours, France. hal-01030745
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Page 1: (Un)conditional consensus emergence under perturbed and ...

HAL Id: hal-01030745https://hal.inria.fr/hal-01030745

Submitted on 22 Jul 2014

HAL is a multi-disciplinary open accessarchive for the deposit and dissemination of sci-entific research documents, whether they are pub-lished or not. The documents may come fromteaching and research institutions in France orabroad, or from public or private research centers.

L’archive ouverte pluridisciplinaire HAL, estdestinée au dépôt et à la diffusion de documentsscientifiques de niveau recherche, publiés ou non,émanant des établissements d’enseignement et derecherche français ou étrangers, des laboratoirespublics ou privés.

(Un)conditional consensus emergence under perturbedand decentralized feedback controlsMattia Bongini, Dante Kalise, Massimo Fornasier

To cite this version:Mattia Bongini, Dante Kalise, Massimo Fornasier. (Un)conditional consensus emergence under per-turbed and decentralized feedback controls. NETCO 2014 - New Trends in Optimal Control, Jun2014, Tours, France. �hal-01030745�

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(Un)conditional consensus emergence underperturbed and decentralized feedback controls

(joint work with D. Kalise and M. Fornasier)

Mattia Bongini

Technische Universitat Munchen,Department of Mathematics,

Chair of Applied Numerical Analysis

[email protected]

Netco 2014Tours

June 23-27, 2014

Mattia Bongini (Un)conditional consensus emergence under feedback controls 1 of 28

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Introduction

Large particle systems arise in many modern applications:

Large Facebook “friendship” network

Dynamical data analysis: R. palustris

protein-protein interaction network

Image halftoning via variational dithering

Computational chemistry: molecule

simulation

Mattia Bongini (Un)conditional consensus emergence under feedback controls 2 of 28

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A framework for social dynamics

We consider large particle systemsof form:⇢

xi = vi,vi = (H ? µN )(xi, vi), i = 1, . . . N,

where µN = 1N

PNj=1 δ(xi,vi).

Several “social forces” encoded inthe interaction kernel H:

⌅ Repulsion-attraction

⌅ Alignment

⌅ ...Patterns related to different balance of social

forces.

Mattia Bongini (Un)conditional consensus emergence under feedback controls 3 of 28

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A framework for social dynamics

We consider large particle systemsof form:⇢

xi = vi,vi = (H ? µN )(xi, vi), i = 1, . . . N,

where µN = 1N

PNj=1 δ(xi,vi).

Several “social forces” encoded inthe interaction kernel H:

⌅ Repulsion-attraction

⌅ Alignment

⌅ ...Patterns related to different balance of social

forces.

Understanding how superposition of re-iterated binary “socialforces” yields global self-organization.

Mattia Bongini (Un)conditional consensus emergence under feedback controls 3 of 28

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Outline of the talk

⌅ Self-organization in free social interactions can fail due to an ex-cess of narrow-mindedness of the social agents;

Mattia Bongini (Un)conditional consensus emergence under feedback controls 4 of 28

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Outline of the talk

⌅ Self-organization in free social interactions can fail due to an ex-cess of narrow-mindedness of the social agents;

⌅ we shall propose a model of narrow-mindedness and show a quan-titative link between the degree of narrow-mindedness in the so-ciety and its convergence to global patterns;

Mattia Bongini (Un)conditional consensus emergence under feedback controls 4 of 28

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Outline of the talk

⌅ Self-organization in free social interactions can fail due to an ex-cess of narrow-mindedness of the social agents;

⌅ we shall propose a model of narrow-mindedness and show a quan-titative link between the degree of narrow-mindedness in the so-ciety and its convergence to global patterns;

⌅ we then explore a different strategy to enforce self-organization,namely sparse control policies, and compare it with the previousdecentralized approach;

Mattia Bongini (Un)conditional consensus emergence under feedback controls 4 of 28

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Outline of the talk

⌅ Self-organization in free social interactions can fail due to an ex-cess of narrow-mindedness of the social agents;

⌅ we shall propose a model of narrow-mindedness and show a quan-titative link between the degree of narrow-mindedness in the so-ciety and its convergence to global patterns;

⌅ we then explore a different strategy to enforce self-organization,namely sparse control policies, and compare it with the previousdecentralized approach;

⌅ finally, we shall see how sparse stabilization techniques can beexported successfully to different models.

Mattia Bongini (Un)conditional consensus emergence under feedback controls 4 of 28

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A framework for consensus emergence

The Cucker-Smale model is obtained by the choice of the interactionkernel H(x, v) = a(|x|)(−v).

8>><>>:

xi = vi 2 Rd

vi =1

N

NX

j=1

a⇣kxi − xjk2

⌘(vj − vi) 2 R

d, for i = 1, . . . N,

where a(r) := aβ(r) = 1(1+r2)β

, β > 0 models the exchange of

information between agents.

Mattia Bongini (Un)conditional consensus emergence under feedback controls 5 of 28

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A framework for consensus emergence

The Cucker-Smale model is obtained by the choice of the interactionkernel H(x, v) = a(|x|)(−v).

8>><>>:

xi = vi 2 Rd

vi =1

N

NX

j=1

a⇣kxi − xjk2

⌘(vj − vi) 2 R

d, for i = 1, . . . N,

where a(r) := aβ(r) = 1(1+r2)β

, β > 0 models the exchange of

information between agents.We say that a solution {(xi, vi)}Ni=1 tends to consensus if there existsa vector w 2 R

d such that

limt!+1

kvi(t)− wk = 0 for every i = 1, . . . , N.

Mattia Bongini (Un)conditional consensus emergence under feedback controls 5 of 28

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Conditional consensus emergence for generic a(·)Consider the symmetric bilinear form

B(u, v) =1

2N2

X

i,j

hui − uj , vi − vji =1

N

NX

i=1

hui, vii − hu, vi,

andX(t) = B(x(t), x(t)), V (t) = B(v(t), v(t)).

Mattia Bongini (Un)conditional consensus emergence under feedback controls 6 of 28

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Conditional consensus emergence for generic a(·)Consider the symmetric bilinear form

B(u, v) =1

2N2

X

i,j

hui − uj , vi − vji =1

N

NX

i=1

hui, vii − hu, vi,

andX(t) = B(x(t), x(t)), V (t) = B(v(t), v(t)).

Theorem (Ha-Ha-Kim)

Let (x0, v0) 2 (Rd)N ⇥ (Rd)N be such thatX0 = B(x0, x0) and V0 = B(v0, v0) satisfyZ 1

pX0

a(p2Nr)dr ≥

pV0 .

Then the solution with initial data (x0, v0)tends to consensus.

Mattia Bongini (Un)conditional consensus emergence under feedback controls 6 of 28

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Conditional consensus emergence for generic a(·)Consider the symmetric bilinear form

B(u, v) =1

2N2

X

i,j

hui − uj , vi − vji =1

N

NX

i=1

hui, vii − hu, vi,

andX(t) = B(x(t), x(t)), V (t) = B(v(t), v(t)).

Theorem (Ha-Ha-Kim)

Let (x0, v0) 2 (Rd)N ⇥ (Rd)N be such thatX0 = B(x0, x0) and V0 = B(v0, v0) satisfyZ 1

pX0

a(p2Nr)dr ≥

pV0 .

Then the solution with initial data (x0, v0)tends to consensus.Hence for a(t) := aβ(t) we have uncondi-tional convergence for 0 β 1

2 .

Mattia Bongini (Un)conditional consensus emergence under feedback controls 6 of 28

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Non-consensus events

If a(·) = aβ(·) and β > 1/2 then the consensus condition is notsatisfied by all (x0, v0) 2 (Rd)N ⇥ (Rd)N , as shown by Cucker andSmale.

Mattia Bongini (Un)conditional consensus emergence under feedback controls 7 of 28

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Non-consensus events

If a(·) = aβ(·) and β > 1/2 then the consensus condition is notsatisfied by all (x0, v0) 2 (Rd)N ⇥ (Rd)N , as shown by Cucker andSmale.Consider β = 1, N = 2, d = 1 and let x(t) = x1(t) − x2(t) andv(t) = v1(t) − v2(t) be the relative positions and velocities of thetwo agents on the line: rewrite the system as8

<:

x = v

v = − v

1 + x2

with initial conditions x(0) = x0 and v(0) = v0 > 0.

Mattia Bongini (Un)conditional consensus emergence under feedback controls 7 of 28

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Non-consensus events

If a(·) = aβ(·) and β > 1/2 then the consensus condition is notsatisfied by all (x0, v0) 2 (Rd)N ⇥ (Rd)N , as shown by Cucker andSmale.Consider β = 1, N = 2, d = 1 and let x(t) = x1(t) − x2(t) andv(t) = v1(t) − v2(t) be the relative positions and velocities of thetwo agents on the line: rewrite the system as8

<:

x = v

v = − v

1 + x2

with initial conditions x(0) = x0 and v(0) = v0 > 0.By direct integration

v(t) = − arctanx(t) + arctanx0 + v0.

Hence, if arctanx0 + v0 > ⇡/2 + " we have

v(t) > ⇡/2 + "− arctanx(t) > ", 8t 2 R+.

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A possible way out...

However, in the work Caponigro-Fornasier-Piccoli–Trelat it is shownthat the addition of an extra term of the form8>><>>:

xi = vi

vi =1

N

NX

j=1

a⇣kxi − xjk2

⌘(vj − vi) + γ(v − vi), for i = 1, . . . N,

where γ > 0, implies convergence to consensus unconditionally.

Mattia Bongini (Un)conditional consensus emergence under feedback controls 8 of 28

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A possible way out...

However, in the work Caponigro-Fornasier-Piccoli–Trelat it is shownthat the addition of an extra term of the form8>><>>:

xi = vi

vi =1

N

NX

j=1

a⇣kxi − xjk2

⌘(vj − vi) + γ(v − vi), for i = 1, . . . N,

where γ > 0, implies convergence to consensus unconditionally.This happens because each agent has an additional stirring to reachthe common goal v.But what happens if every agent has its own “local” goal?

Mattia Bongini (Un)conditional consensus emergence under feedback controls 8 of 28

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Introducing decentralized controls

We study how the convergence to consensus is modified by the in-troduction of the following extra term8>><>>:

xi = vi

vi =1

N

NX

j=1

a⇣kxi − xjk2

⌘(vj − vi) + γ(vRi − vi), for i = 1, . . . N,

where γ > 0 and

vRi =1

PNk=1 χ[0,R](kxi − xkk)

NX

j=1

χ[0,R](kxi − xjk)vj ,

is the local mean velocity calculated by the i-th agent taking intoaccount only the agents inside a ball of radius R centered on him.

Mattia Bongini (Un)conditional consensus emergence under feedback controls 9 of 28

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Introducing decentralized controls

We study how the convergence to consensus is modified by the in-troduction of the following extra term8>><>>:

xi = vi

vi =1

N

NX

j=1

a⇣kxi − xjk2

⌘(vj − vi) + γ(vRi − vi), for i = 1, . . . N,

where γ > 0 and

vRi =1

PNk=1 χ[0,R](kxi − xkk)

NX

j=1

χ[0,R](kxi − xjk)vj ,

is the local mean velocity calculated by the i-th agent taking intoaccount only the agents inside a ball of radius R centered on him.GOAL: Study the behavior of the system for R ! 0 and R ! +1.

Mattia Bongini (Un)conditional consensus emergence under feedback controls 9 of 28

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Behavior of the modified system in function of R

−15 −10 −5 0 5 10 15−15

−10

−5

0

5

10

152D flock trajectories, N=40 and R=0 (uncontrolled)

−8 −6 −4 −2 0 2 4 6 8−8

−6

−4

−2

0

2

4

6

82D flock trajectories, N=40 and R=2

−8 −6 −4 −2 0 2 4 6 8−8

−6

−4

−2

0

2

4

6

82D flock trajectories, N=40 and R=1

−8 −6 −4 −2 0 2 4 6 8−8

−6

−4

−2

0

2

4

6

82D flock trajectories, N=40 and R=3

Mattia Bongini (Un)conditional consensus emergence under feedback controls 10 of 28

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A different approach

To avoid the issues coming from a normalizing factor varying fromagent to agent, in our study of the asymptotic behavior we replaceit with a function ⌘R(t) 2 L1([0,+1)) satisfying

limR!0

ηR(t) = 1

= limR!0

NX

k=1

χ[0,R](kxi(t)− xk(t)k) for every i

!

,

limR!+1

ηR(t) = N

= limR!+1

NX

k=1

χ[0,R](kxi(t)− xk(t)k) for every i

!

,

Mattia Bongini (Un)conditional consensus emergence under feedback controls 11 of 28

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A different approach

To avoid the issues coming from a normalizing factor varying fromagent to agent, in our study of the asymptotic behavior we replaceit with a function ⌘R(t) 2 L1([0,+1)) satisfying

limR!0

ηR(t) = 1

= limR!0

NX

k=1

χ[0,R](kxi(t)− xk(t)k) for every i

!

,

limR!+1

ηR(t) = N

= limR!+1

NX

k=1

χ[0,R](kxi(t)− xk(t)k) for every i

!

,

like

ηR(t) = maxi=1,...,N

(NX

k=1

χ[0,R](kxi(t)− xk(t)k)

)

.

Mattia Bongini (Un)conditional consensus emergence under feedback controls 11 of 28

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A different approach

To avoid the issues coming from a normalizing factor varying fromagent to agent, in our study of the asymptotic behavior we replaceit with a function ⌘R(t) 2 L1([0,+1)) satisfying

limR!0

ηR(t) = 1

= limR!0

NX

k=1

χ[0,R](kxi(t)− xk(t)k) for every i

!

,

limR!+1

ηR(t) = N

= limR!+1

NX

k=1

χ[0,R](kxi(t)− xk(t)k) for every i

!

,

like

ηR(t) = maxi=1,...,N

(NX

k=1

χ[0,R](kxi(t)− xk(t)k)

)

.

Hence, we replace vRi in the system with

vRi =

1

ηR

NX

k=1

χ[0,R](kxi − xkk)vj .

Mattia Bongini (Un)conditional consensus emergence under feedback controls 11 of 28

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A sufficient condition

TheoremReplace vRi with vRi in the model. Let (x0, v0) 2 (Rd)N ⇥ (Rd)N

and define X0 = B(x0, x0) and V0 = B(v0, v0). Then the solutionwith initial data (x0, v0) tends to consensus if one of the followingis satisfied:

Mattia Bongini (Un)conditional consensus emergence under feedback controls 12 of 28

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A sufficient condition

TheoremReplace vRi with vRi in the model. Let (x0, v0) 2 (Rd)N ⇥ (Rd)N

and define X0 = B(x0, x0) and V0 = B(v0, v0). Then the solutionwith initial data (x0, v0) tends to consensus if one of the followingis satisfied:

p2NX0 R and

R1pX0

a(p2Nr)dr + γ

⇣Rp2N

−pX0

⌘≥

pV0;

Mattia Bongini (Un)conditional consensus emergence under feedback controls 12 of 28

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A sufficient condition

TheoremReplace vRi with vRi in the model. Let (x0, v0) 2 (Rd)N ⇥ (Rd)N

and define X0 = B(x0, x0) and V0 = B(v0, v0). Then the solutionwith initial data (x0, v0) tends to consensus if one of the followingis satisfied:

p2NX0 R and

R1pX0

a(p2Nr)dr + γ

⇣Rp2N

−pX0

⌘≥

pV0;

p2NX0 > R and

R1pX0

a(p2Nr)dr ≥

pV0.

Mattia Bongini (Un)conditional consensus emergence under feedback controls 12 of 28

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A sufficient condition

TheoremReplace vRi with vRi in the model. Let (x0, v0) 2 (Rd)N ⇥ (Rd)N

and define X0 = B(x0, x0) and V0 = B(v0, v0). Then the solutionwith initial data (x0, v0) tends to consensus if one of the followingis satisfied:

p2NX0 R and

R1pX0

a(p2Nr)dr + γ

⇣Rp2N

−pX0

⌘≥

pV0;

p2NX0 > R and

R1pX0

a(p2Nr)dr ≥

pV0.

Proof.via the Ha-Ha-Kim Theorem.

Mattia Bongini (Un)conditional consensus emergence under feedback controls 12 of 28

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A sufficient condition

TheoremReplace vRi with vRi in the model. Let (x0, v0) 2 (Rd)N ⇥ (Rd)N

and define X0 = B(x0, x0) and V0 = B(v0, v0). Then the solutionwith initial data (x0, v0) tends to consensus if one of the followingis satisfied:

p2NX0 R and

R1pX0

a(p2Nr)dr + γ

⇣Rp2N

−pX0

⌘≥

pV0;

p2NX0 > R and

R1pX0

a(p2Nr)dr ≥

pV0.

Proof.via the Ha-Ha-Kim Theorem.

⌅ Result generalizable to different forms of ⌘R and χ[0,R].

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Variation of the empirical and theoretical consensusregion in function of R

Empirical probability of consensus, N=20 and R=1

X0

V0

0 2 4 6 8 100

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0

0.2

0.4

0.6

0.8

1

Empirical probability of consensus, N=20 and R=2

X0

V0

0 2 4 6 8 100

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0

0.2

0.4

0.6

0.8

1

X0

V0

Theoretical consensus region, N=20 and R=1

0 0.2 0.4 0.6 0.8 10

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0.04

X0

V0

Theoretical consensus region, N=20 and R=2

0 0.2 0.4 0.6 0.8 10

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0.04

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Sharpness of the result for N = 2

X0

V0

Empirical probability of consensus, N=2 and R=0

0 2 4 6 8 100

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0

0.2

0.4

0.6

0.8

1

Empirical probability of consensus, N=2 and R=2

X0

V0

0 2 4 6 8 100

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0

0.2

0.4

0.6

0.8

1

X0

V0

Theoretical consensus, N=2 and R=0

0 2 4 6 8 100

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

X0

V0

Theoretical consensus, N=2 and R=2

0 1 2 3 4 5 6 7 8 9 100

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

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Efficiency of stabilization

⌅ We have shown that an unconditional (w.r.t. the initial data)convergence to consensus is guaranteed only in the case R = 1,i.e., the agents are completely “open-minded”.In this case, the Lyapunov functional V decreases at least as

V (t) V (0)eγt.

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Efficiency of stabilization

⌅ We have shown that an unconditional (w.r.t. the initial data)convergence to consensus is guaranteed only in the case R = 1,i.e., the agents are completely “open-minded”.In this case, the Lyapunov functional V decreases at least as

V (t) V (0)eγt.

⌅ Question: are there more economical and efficient strategies whichguarantees unconditional stabilization?

Mattia Bongini (Un)conditional consensus emergence under feedback controls 15 of 28

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Efficiency of stabilization

⌅ We have shown that an unconditional (w.r.t. the initial data)convergence to consensus is guaranteed only in the case R = 1,i.e., the agents are completely “open-minded”.In this case, the Lyapunov functional V decreases at least as

V (t) V (0)eγt.

⌅ Question: are there more economical and efficient strategies whichguarantees unconditional stabilization?

⌅ More precisely, we wish to make the quantity ddtV (t) the smallest

possible and use the minimal amount of intervention (e.g., byimposing sparsifying constraints).

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Self-organization vs organization by intervention

We introduce a control term in the Cucker-Smale model:8>><>>:

xi = vi

vi =1

N

NX

j=1

a(kxj − xik)(vj − vi) + ui, for i = 1, . . . , N.

The admissible controls will be measurable functions u = (u1, . . . , uN ) :[0,+1) ! R

N such thatPN

i=1 kui(t)k M for every t > 0, for agiven constant M .

Mattia Bongini (Un)conditional consensus emergence under feedback controls 16 of 28

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Self-organization vs organization by intervention

We introduce a control term in the Cucker-Smale model:8>><>>:

xi = vi

vi =1

N

NX

j=1

a(kxj − xik)(vj − vi) + ui, for i = 1, . . . , N.

The admissible controls will be measurable functions u = (u1, . . . , uN ) :[0,+1) ! R

N such thatPN

i=1 kui(t)k M for every t > 0, for agiven constant M .

Our aim is then to find admissiblecontrols steering the system to theconsensus region and minimizing

R(t, u) := R(t) =d

dtV (t),

in a large class of controls.

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Greedy sparse control

Theorem (Caponigro-Fornasier-Piccoli-Trelat)

For every initial condition (x0, v0) 2 (Rd)N ⇥ (Rd)N and M > 0there exist T > 0 and a sparse control u : [0, T ] ! (Rd)N , withPN

i=1 kui(t)k M for every t 2 [0, T ] such that the associated solu-tion tends to consensus.

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Greedy sparse control

Theorem (Caponigro-Fornasier-Piccoli-Trelat)

For every initial condition (x0, v0) 2 (Rd)N ⇥ (Rd)N and M > 0there exist T > 0 and a sparse control u : [0, T ] ! (Rd)N , withPN

i=1 kui(t)k M for every t 2 [0, T ] such that the associated solu-tion tends to consensus.We can choose adaptively the control law explicitly as one of thesolutions of the variational problem

minB(v, u) +T (x)

N

NX

i=1

kuik subject to

NX

i=1

kuik M ,

where

T (x) =

Z ∞

pB(x,x)

a(p2Nr)dr (threshold function by Ha-Ha-Kim)

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The 1-sparse feedback strategy

DefinitionFor every t ≥ 0 we define the 1-sparse feedback control as

ui(t) =

(−M

v⊥

i (t)

kv⊥

i(t)k

if i = bι(t)0 if i 6= bι(t)

where b◆(t) 2 {1, . . . , N} is the minimum index such that

kv⊥bι(t)(t)k = maxj=1,...,N kv⊥j (t)k.

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The 1-sparse feedback strategy

DefinitionFor every t ≥ 0 we define the 1-sparse feedback control as

ui(t) =

(−M

v⊥

i (t)

kv⊥

i(t)k

if i = bι(t)0 if i 6= bι(t)

where b◆(t) 2 {1, . . . , N} is the minimum index such that

kv⊥bι(t)(t)k = maxj=1,...,N kv⊥j (t)k.

TheoremThe 1-sparse control is the mini-mizer of

R(t, u) := R(t) =d

dtV (t),

among all the solution of the varia-tional problem.

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The 1-sparse feedback strategy

DefinitionFor every t ≥ 0 we define the 1-sparse feedback control as

ui(t) =

(−M

v⊥

i (t)

kv⊥

i(t)k

if i = bι(t)0 if i 6= bι(t)

where b◆(t) 2 {1, . . . , N} is the minimum index such that

kv⊥bι(t)(t)k = maxj=1,...,N kv⊥j (t)k.

TheoremThe 1-sparse control is the mini-mizer of

R(t, u) := R(t) =d

dtV (t),

among all the solution of the varia-tional problem.

The control acts on the

most “stubborn” agent. We

may call it the “shepherd

dog strategy”

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Dynamical systems driven by attraction andrepulsion forces

The Cucker-Dong model: for every 1 i N8>>><

>>>:

xi = vi 2 Rd

vi = −bivi +

NX

j=1

a(kxi − xjk

2) (xj − xi) +

NX

j=1

j 6=i

f(kxi − xjk

2) (xi − xj) 2 Rd

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Dynamical systems driven by attraction andrepulsion forces

The Cucker-Dong model: for every 1 i N8>>><

>>>:

xi = vi 2 Rd

vi = −bivi +

NX

j=1

a(kxi − xjk

2) (xj − xi) +

NX

j=1

j 6=i

f(kxi − xjk

2) (xi − xj) 2 Rd

where

⌅ bi : [0,+1) ! [0,Λ] is the friction acting on the system,

Mattia Bongini (Un)conditional consensus emergence under feedback controls 19 of 28

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Dynamical systems driven by attraction andrepulsion forces

The Cucker-Dong model: for every 1 i N8>>><

>>>:

xi = vi 2 Rd

vi = −bivi +

NX

j=1

a(kxi − xjk

2) (xj − xi) +

NX

j=1

j 6=i

f(kxi − xjk

2) (xi − xj) 2 Rd

where

⌅ bi : [0,+1) ! [0,Λ] is the friction acting on the system,

⌅ a : [0,+1) ! [0,+1) is the rate of communication,

Mattia Bongini (Un)conditional consensus emergence under feedback controls 19 of 28

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Dynamical systems driven by attraction andrepulsion forces

The Cucker-Dong model: for every 1 i N8>>><

>>>:

xi = vi 2 Rd

vi = −bivi +

NX

j=1

a(kxi − xjk

2) (xj − xi) +

NX

j=1

j 6=i

f(kxi − xjk

2) (xi − xj) 2 Rd

where

⌅ bi : [0,+1) ! [0,Λ] is the friction acting on the system,

⌅ a : [0,+1) ! [0,+1) is the rate of communication,

⌅ f : (0,+1) ! (0,+1) such that

Z +1

δ

f(r) dr < 1 for every δ > 0,

Z +1

0f(r) dr = +1

models the repulsion between agents.

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Example: Lennard-Jones potential

⌅ It is the potential of the Van der Waals force.

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Example: Lennard-Jones potential

⌅ It is the potential of the Van der Waals force.⌅ It can be seen as a Cucker-Dong system with

a(r) =σa

r7and f(r) =

σf

r13.

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Example: Lennard-Jones potential

⌅ It is the potential of the Van der Waals force.⌅ It can be seen as a Cucker-Dong system with

a(r) =σa

r7and f(r) =

σf

r13.

Difference f(r)− a(r) for Lennard-Jones potentials.

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Total Energy of Cucker-Dong Systems

We introduce

⌅ the kinetic energy K(t) := 12

PNi=1 kvi(t)k

2,

Mattia Bongini (Un)conditional consensus emergence under feedback controls 21 of 28

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Total Energy of Cucker-Dong Systems

We introduce

⌅ the kinetic energy K(t) := 12

PNi=1 kvi(t)k

2,

⌅ the potential energy

P (t) :=1

2

NX

i,j=1

i 6=j

Z kxi(t)−xj(t)k2

0a(r)dr +

1

2

NX

i,j=1

i 6=j

Z 1

kxi(t)−xj(t)k2f(r)dr,

Mattia Bongini (Un)conditional consensus emergence under feedback controls 21 of 28

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Total Energy of Cucker-Dong Systems

We introduce

⌅ the kinetic energy K(t) := 12

PNi=1 kvi(t)k

2,

⌅ the potential energy

P (t) :=1

2

NX

i,j=1

i 6=j

Z kxi(t)−xj(t)k2

0a(r)dr +

1

2

NX

i,j=1

i 6=j

Z 1

kxi(t)−xj(t)k2f(r)dr,

⌅ the total energy E(t) := K(t) + P (t).

Mattia Bongini (Un)conditional consensus emergence under feedback controls 21 of 28

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Conditional consensus emergence

Theorem (Cucker - Dong)Consider a population of N agents modeled by a Cucker-Dong sys-tem with a(t) := aβ(t) =

1(1+t2)β

, β > 0

kxi(0)− xj(0)k > 0 for all i 6= j.

Then there exists a unique solution (x(t), v(t)) of the system withinitial state (x(0), v(0)). Moreover if one of the two following hy-potheses holds:

Mattia Bongini (Un)conditional consensus emergence under feedback controls 22 of 28

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Conditional consensus emergence

Theorem (Cucker - Dong)Consider a population of N agents modeled by a Cucker-Dong sys-tem with a(t) := aβ(t) =

1(1+t2)β

, β > 0

kxi(0)− xj(0)k > 0 for all i 6= j.

Then there exists a unique solution (x(t), v(t)) of the system withinitial state (x(0), v(0)). Moreover if one of the two following hy-potheses holds:

1. β 1

Mattia Bongini (Un)conditional consensus emergence under feedback controls 22 of 28

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Conditional consensus emergence

Theorem (Cucker - Dong)Consider a population of N agents modeled by a Cucker-Dong sys-tem with a(t) := aβ(t) =

1(1+t2)β

, β > 0

kxi(0)− xj(0)k > 0 for all i 6= j.

Then there exists a unique solution (x(t), v(t)) of the system withinitial state (x(0), v(0)). Moreover if one of the two following hy-potheses holds:

1. β 1

2. β > 1 and E(0) < # := (N − 1)R10 a(r)dr

Mattia Bongini (Un)conditional consensus emergence under feedback controls 22 of 28

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Conditional consensus emergence

Theorem (Cucker - Dong)Consider a population of N agents modeled by a Cucker-Dong sys-tem with a(t) := aβ(t) =

1(1+t2)β

, β > 0

kxi(0)− xj(0)k > 0 for all i 6= j.

Then there exists a unique solution (x(t), v(t)) of the system withinitial state (x(0), v(0)). Moreover if one of the two following hy-potheses holds:

1. β 1

2. β > 1 and E(0) < # := (N − 1)R10 a(r)dr

then the population is cohesive and collision-avoiding, i.e., thereexist two constants B0 and b0 > 0 such that, for every t ≥ 0

b0 kxi(t)− xj(t)k B0 for all 1 i 6= j N.

Mattia Bongini (Un)conditional consensus emergence under feedback controls 22 of 28

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Non-consensus events need intervention

β 1 β > 1 and E(0) ≥ ϑ

Mattia Bongini (Un)conditional consensus emergence under feedback controls 23 of 28

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Non-consensus events need intervention

β 1 β > 1 and E(0) ≥ ϑ

⌅ Assume we are in the case β > 1 and E(0) ≥ #. Can we againstabilize the society by external parsimonious intervention?

Mattia Bongini (Un)conditional consensus emergence under feedback controls 23 of 28

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Non-consensus events need intervention

β 1 β > 1 and E(0) ≥ ϑ

⌅ Assume we are in the case β > 1 and E(0) ≥ #. Can we againstabilize the society by external parsimonious intervention?

⌅ We again introduce a control term inside the model8>>><

>>>:

xi = vi

vi = −bivi +

NX

j=1

a(kxi − xjk

2) (xj − xi) +

NX

j=1

j 6=i

f(kxi − xjk

2) (xi − xj) + ui

under the sparsifying constraintPN

i=1 kui(t)k M for M > 0.

Mattia Bongini (Un)conditional consensus emergence under feedback controls 23 of 28

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Sparse control strategy for the Cucker-Dong model

DefinitionFor every t ≥ 0 we define the 1-sparse feedback control as

ui(t) =

(− M

E(0)E(t) vi(t)

kvi(t)kif i = bι(t)

0 if i 6= bι(t)

where b◆(t) 2 {1, . . . , N} is the minimum index such that

kvbι(t)(t)k = maxj=1,...,N kvj(t)k.

Mattia Bongini (Un)conditional consensus emergence under feedback controls 24 of 28

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Sparse control strategy for the Cucker-Dong model

DefinitionFor every t ≥ 0 we define the 1-sparse feedback control as

ui(t) =

(− M

E(0)E(t) vi(t)

kvi(t)kif i = bι(t)

0 if i 6= bι(t)

where b◆(t) 2 {1, . . . , N} is the minimum index such that

kvbι(t)(t)k = maxj=1,...,N kvj(t)k.

Define for every t > 0 the set

K(t) :=

(

u 2 (Rd)N |NX

i=1

kuik M ·E(t)

E(0)

)

,

and for every t > 0 and q > 0 the functional Jt,q : (Rd)N ! R

Jt,q(u) = hv(t), ui+

∥∥∥ 1N

PN

i=1 vi(0)∥∥∥

q

NX

i=1

kuik .

Mattia Bongini (Un)conditional consensus emergence under feedback controls 24 of 28

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Under the following hypotheses...

TheoremFix M > 0. Let (x0, v0) 2 (Rd)N ⇥ (Rd)N be such that the followinghold:

1. kx0i − x0jk > 0 for all i 6= j,

Mattia Bongini (Un)conditional consensus emergence under feedback controls 25 of 28

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Under the following hypotheses...

TheoremFix M > 0. Let (x0, v0) 2 (Rd)N ⇥ (Rd)N be such that the followinghold:

1. kx0i − x0jk > 0 for all i 6= j,

2. k 1N

PNi=1 vi(0)k > 0,

Mattia Bongini (Un)conditional consensus emergence under feedback controls 25 of 28

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Under the following hypotheses...

TheoremFix M > 0. Let (x0, v0) 2 (Rd)N ⇥ (Rd)N be such that the followinghold:

1. kx0i − x0jk > 0 for all i 6= j,

2. k 1N

PNi=1 vi(0)k > 0,

3. E(0) ≥ # > E(0) exp

−2

p3

9

Mk 1N

PNi=1 vi(0)k3

E(0)p

E(0)⇣

Λp

E(0)+MN

!.

Then...

Mattia Bongini (Un)conditional consensus emergence under feedback controls 25 of 28

Page 65: (Un)conditional consensus emergence under perturbed and ...

... we can prove the following.

Theorem (continues...)

... then there exist T > 0 and q > 0 such that

⌅ the 1-sparse feedback control belongs to the set argminu2K(t) Jt,q(u)for every t T ;

Mattia Bongini (Un)conditional consensus emergence under feedback controls 26 of 28

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... we can prove the following.

Theorem (continues...)

... then there exist T > 0 and q > 0 such that

⌅ the 1-sparse feedback control belongs to the set argminu2K(t) Jt,q(u)for every t T ;

⌅ the 1-sparse feedback control is an instantaneous minimizer of thefunctional

D(t, u) =d

dtE(t)

over all possible feedback controls in argminu2K(t) Jt,q(u);

Mattia Bongini (Un)conditional consensus emergence under feedback controls 26 of 28

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... we can prove the following.

Theorem (continues...)

... then there exist T > 0 and q > 0 such that

⌅ the 1-sparse feedback control belongs to the set argminu2K(t) Jt,q(u)for every t T ;

⌅ the 1-sparse feedback control is an instantaneous minimizer of thefunctional

D(t, u) =d

dtE(t)

over all possible feedback controls in argminu2K(t) Jt,q(u);

⌅ there exists a solution of the controlled Cucker-Dong system as-sociated to a control solving the variational problem

eu 2 argminu∈K(t)

Jt,q(u) for every t T.

Mattia Bongini (Un)conditional consensus emergence under feedback controls 26 of 28

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Summing up our results

⌅ We have shown a quantitative link between a degree of “narrow-mindedness” and convergence to global patterns;

Mattia Bongini (Un)conditional consensus emergence under feedback controls 27 of 28

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Summing up our results

⌅ We have shown a quantitative link between a degree of “narrow-mindedness” and convergence to global patterns;

⌅ a sparse control strategy is more efficient than local decentralizedcontrol in order to enforce convergence: if we pay our attentionsolely to the “most stubborn” agent while leaving the other freeto adjust themselves, we actually have the “best greedy” strategy;

Mattia Bongini (Un)conditional consensus emergence under feedback controls 27 of 28

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Summing up our results

⌅ We have shown a quantitative link between a degree of “narrow-mindedness” and convergence to global patterns;

⌅ a sparse control strategy is more efficient than local decentralizedcontrol in order to enforce convergence: if we pay our attentionsolely to the “most stubborn” agent while leaving the other freeto adjust themselves, we actually have the “best greedy” strategy;

⌅ in contrast to what happen with the Cucker-Smale model, theresult for the 1-sparse control feedback in the Cucker-Dong modelis conditional (it depends on the initial conditions of the system)

Mattia Bongini (Un)conditional consensus emergence under feedback controls 27 of 28

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Summing up our results

⌅ We have shown a quantitative link between a degree of “narrow-mindedness” and convergence to global patterns;

⌅ a sparse control strategy is more efficient than local decentralizedcontrol in order to enforce convergence: if we pay our attentionsolely to the “most stubborn” agent while leaving the other freeto adjust themselves, we actually have the “best greedy” strategy;

⌅ in contrast to what happen with the Cucker-Smale model, theresult for the 1-sparse control feedback in the Cucker-Dong modelis conditional (it depends on the initial conditions of the system)) we don’t know if the conditions are necessary.

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A few info

⌅ WWW: http://www-m15.ma.tum.de/

⌅ References:⇤ M. Bongini, D. Kalise, and M. Fornasier, (Un)conditional consen-

sus emergence under perturbed and decentralized feedback controls,submitted to Discrete and Continuous Dynamical Systems, pp. 27

⇤ M. Bongini and M. Fornasier, Sparse stabilization of dynamical sys-tems driven by attraction and avoidance forces, Networks and Het-erogeneous Media, Pages 1 - 31, Volume 9, Issue 1, March 2014

⇤ M. Caponigro, M. Fornasier, B. Piccoli, and E. Trelat, Sparse stabi-lization and control of alignment models, to appear in MathematicalModels and Methods in Applied Sciences, pp. 33

⇤ F. Cucker and J. Dong, A conditional, collision-avoiding, model forswarming, IEEE Trans. Automat. Control, 56(5):1124–1129, 2011

⇤ S.-Y. Ha, T. Ha, and J.-H. Kim, Emergent behavior of a Cucker-Smale type particle model with nonlinear velocity couplings, IEEETrans. Aut. Contr. 55.7 (2010): 1679-1683

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