new hyperbolic set covering problems with competing ground-set … · 2013. 1. 20. · hyperbolic...
TRANSCRIPT
g
Hyperbolic set covering problems
with competing ground-set elements
Edoardo Amaldi, Sandro Bosio and Federico Malucelli
Dipartimento di Elettronica e Informazione (DEI), Politecnico di Milano, Italy
XI Workshop on Combinatorial Optimization, Aussois, 2007
.
Outline g
Problems definition
The motivating application: Wireless Local Area Network design
Hyperbolic integer programming formulation
Complexity and Approximability results
Linearizations and Lagrangean Relaxation
Ongoing work and concluding remarks
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Set Covering notation g
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Set Covering notation g
I
I: afinite groundset
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Set Covering notation g
J
I: afinite groundset
J : acollectionof subsetsJ = {Ij ⊆ I : j ∈ J}
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Set Covering notation g
i
Ji
I: afinite groundset
J : acollectionof subsetsJ = {Ij ⊆ I : j ∈ J}
Ji ⊆ J : subcollection of the subsetscovering an elementi ∈ I
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Set Covering notation g
S
I: afinite groundset
J : acollectionof subsetsJ = {Ij ⊆ I : j ∈ J}
Ji ⊆ J : subcollection of the subsetscovering an elementi ∈ I
coverS: a subcollection indexed byS ⊆ J such that⋃
j∈S Ij = I
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Set Covering problems g
Classical Set Covering Problem (SCP):
Given an instance(I,J ) and a costcj ∈ R for eachj ∈ J ,
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Set Covering problems g
Classical Set Covering Problem (SCP):
Given an instance(I,J ) and a costcj ∈ R for eachj ∈ J ,
find acoverS that minimizes thetotal costc(S) =∑
j∈S
cj
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Set Covering problems g
Classical Set Covering Problem (SCP):
Given an instance(I,J ) and a costcj ∈ R for eachj ∈ J ,
find acoverS that minimizes thetotal costc(S) =∑
j∈S
cj
Variants: Set Partitioning forbiddenoverlap
Set Multicover requiredoverlap
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Set Covering problems g
Classical Set Covering Problem (SCP):
Given an instance(I,J ) and a costcj ∈ R for eachj ∈ J ,
find acoverS that minimizes thetotal costc(S) =∑
j∈S
cj
Variants: Set Partitioning forbiddenoverlap
Set Multicover requiredoverlap
Also: Quadratic objective functions
Maximum coverage
...
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Coverage share g
Given a covering instance(I,J ), a coverS and an elementi ∈ I
coverage share: r(S, i) =1
1 + |Ni(S)|
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Coverage share g
Given a covering instance(I,J ), a coverS and an elementi ∈ I
coverage share: r(S, i) =1
1 + |Ni(S)|
S
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Coverage share g
Given a covering instance(I,J ), a coverS and an elementi ∈ I
coverage share: r(S, i) =1
1 + |Ni(S)|
i
Ni
r(S,i)= 1
3
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Coverage share g
Given a covering instance(I,J ), a coverS and an elementi ∈ I
coverage share: r(S, i) =1
1 + |Ni(S)|
i
Ni
r(S,i)= 1
7
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Coverage share g
Given a covering instance(I,J ), a coverS and an elementi ∈ I
coverage share: r(S, i) =1
1 + |Ni(S)|
i
Ni
r(S,i)= 1
7
Fraction of resource received byi assumingfair allocation
among thecompeting elements(neighbors ofi)
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Coverage share problems g
Maximum Total Coverage Share Problem (TCSP):
Given an instance(I,J ), find acoverS thatmaximizes
ft(S) =∑
i∈I
1
1 + |Ni(S)|
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Coverage share problems g
Maximum Total Coverage Share Problem (TCSP):
Given an instance(I,J ), find acoverS thatmaximizes
ft(S) =∑
i∈I
1
1 + |Ni(S)|
Maximum Minimum Coverage Share Problem (MCSP):
Given an instance(I,J ), find acoverS thatmaximizes
fm(S) = mini∈I
1
1 + |Ni(S)|
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Coverage share problems g
Maximum Total Coverage Share Problem (TCSP):
Given an instance(I,J ), find acoverS thatmaximizes
ft(S) =∑
i∈I
1
1 + |Ni(S)|
Maximum Minimum Coverage Share Problem (MCSP):
Given an instance(I,J ), find acoverS thatmaximizes
fm(S) = mini∈I
1
1 + |Ni(S)|
Set covering problems withcompetingground-set elements
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Coverage share problems g
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Coverage share problems g
Instance
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Coverage share problems g
Instance SCP opt
|S| = 2
ft(S) = 1.40
fm(S) =1
11
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Coverage share problems g
Instance SCP opt TCSP opt
|S| = 2
ft(S) = 1.40
fm(S) =1
11
|S| = 4
ft(S) = 3.64
fm(S) =1
7
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Coverage share problems g
Instance SCP opt TCSP opt MCSP opt
|S| = 2
ft(S) = 1.40
fm(S) =1
11
|S| = 4
ft(S) = 3.64
fm(S) =1
7
|S| = 4
ft(S) = 3.42
fm(S) =1
4
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Coverage share problems g
Instance SCP opt TCSP opt MCSP opt
|S| = 2
ft(S) = 1.40
fm(S) =1
11
|S| = 4
ft(S) = 3.64
fm(S) =1
7
|S| = 4
ft(S) = 3.42
fm(S) =1
4
Privilege covers whose subsets havesmall cardinalityandlimited overlaps.
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Wireless Local Area Network g
IEEE 802.11 WLAN: a set ofAccess Pointseach able of serving a set ofusers
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Wireless Local Area Network g
IEEE 802.11 WLAN: a set ofAccess Pointseach able of serving a set ofusers
WLANs are becoming pervasive in airports, trains and train stations, private companies,
universities, hotels, ...
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Wireless Local Area Network g
IEEE 802.11 WLAN: a set ofAccess Pointseach able of serving a set ofusers
Medium Access Control (MAC) Protocol:
A user can access the network if and only ifno other user
is interferingdirectly or indirectly
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Wireless Local Area Network g
IEEE 802.11 WLAN: a set ofAccess Pointseach able of serving a set ofusers
Medium Access Control (MAC) Protocol:
A user can access the network if and only ifno other user
is interferingdirectly or indirectly
Assuming uniformpeaktraffic andfair access after collision,
coverage shareof elementi ≈ fraction of timeused by useri
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Wireless Local Area Network g
IEEE 802.11 WLAN: a set ofAccess Pointseach able of serving a set ofusers
Due to protocol issues, increasing sizes of deployed WLANs and limited resources,
and optimization models and methods can be
very usefulto support the planning decisions.
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Previous and related work g
WLAN design:
Large-scale WLAN design (Hills 01, ...)
Max average signal quality in test points (Rodrigues, Mateus and Loureiro 00/01)
Max coverage level (Kamenetsky and Unbehaun 02)
Max capacity based on constraint satisfaction (Prommak et al. 02)
...
First hyperbolic model and heuristics (Amaldi, Capone, Cesana and Malucelli 04)
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Integer programming formulations g
max∑
i∈I
1
1 + |Ni(S)|
( TCSP) s.t.⋃
j∈S
Ij = I complete coverage
S ⊆ J select subcollection
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Integer programming formulations g
max∑
i∈I
1
1 + |Ni(S)|
( TCSP) s.t.⋃
j∈S
Ij = I complete coverage
S ⊆ J select subcollection
Variables:
xj = 1 if subsetIj is selected (0 otherwise)
yih = 1 if elementsi andh are neighbors (0 otherwise)
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Integer programming formulations g
max∑
i∈I
1
1 +∑
h∈Ni
yih
( TCSP) s.t.∑
j∈Ji
xj ≥ 1 i ∈ I
yih ≥ xj i ∈ I, h ∈ Ni, j ∈ Ji ∩ Jh
yih ≤∑
j∈Ji∩Jh
xj i ∈ I, h ∈ Ni
xj ∈ {0, 1} j ∈ J
yih ∈ {0, 1} i ∈ I, h ∈ Ni
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Integer programming formulations g
max∑
i∈I
1
1 +∑
h∈Ni
yih
→ 0-1 hyperbolic sumproblem
( TCSP) s.t.∑
j∈Ji
xj ≥ 1 i ∈ I
yih ≥ xj i ∈ I, h ∈ Ni, j ∈ Ji ∩ Jh
yih ≤∑
j∈Ji∩Jh
xj i ∈ I, h ∈ Ni
xj ∈ {0, 1} j ∈ J
yih ∈ {0, 1} i ∈ I, h ∈ Ni
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Integer programming formulations g
max mini∈I
1
1 +∑
h∈Ni
yih
(MCSP) s.t.∑
j∈Ji
xj ≥ 1 i ∈ I
yih ≥ xj i ∈ I, h ∈ Ni, j ∈ Ji ∩ Jh
yih ≤∑
j∈Ji∩Jh
xj i ∈ I, h ∈ Ni
xj ∈ {0, 1} j ∈ J
yih ∈ {0, 1} i ∈ I, h ∈ Ni
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Integer programming formulations g
max mini∈I
1
1 +∑
h∈Ni
yih
=1
1 + min maxi∈I
∑
h∈Ni
yih
(MCSP) s.t.∑
j∈Ji
xj ≥ 1 i ∈ I
yih ≥ xj i ∈ I, h ∈ Ni, j ∈ Ji ∩ Jh
yih ≤∑
j∈Ji∩Jh
xj i ∈ I, h ∈ Ni
xj ∈ {0, 1} j ∈ J
yih ∈ {0, 1} i ∈ I, h ∈ Ni
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Connection with Quadratic SCP g
Quadratic Set Covering Problem (QSCP):
Given(I,J ), Q = {qjℓ ∈ R : j, ℓ ∈ J} (wlog symmetric with zero diagonal)
andc = {cj ∈ R : j ∈ J}, find acoverS ⊆ J thatmaximizes
q(S) =1
2
∑
j∈S
∑
ℓ∈S
qjℓ +∑
j∈S
cj
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Connection with Quadratic SCP g
Quadratic Set Covering Problem (QSCP):
Given(I,J ), Q = {qjℓ ∈ R : j, ℓ ∈ J} (wlog symmetric with zero diagonal)
andc = {cj ∈ R : j ∈ J}, find acoverS ⊆ J thatmaximizes
q(S) =1
2
∑
j∈S
∑
ℓ∈S
qjℓ +∑
j∈S
cj
Choice:
cj =∑
i∈Ij
1
|Ij |qjℓ =
∑
i∈Ij∩Iℓ
(
1
|Ij ∪ Iℓ|−
1
|Ij |−
1
|Iℓ|
)
(for j 6= ℓ)
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Connection with Quadratic SCP g
Quadratic Set Covering Problem (QSCP):
Given(I,J ), Q = {qjℓ ∈ R : j, ℓ ∈ J} (wlog symmetric with zero diagonal)
andc = {cj ∈ R : j ∈ J}, find acoverS ⊆ J thatmaximizes
q(S) =1
2
∑
j∈S
∑
ℓ∈S
qjℓ +∑
j∈S
cj
Choice:
cj =∑
i∈Ij
1
|Ij |qjℓ =
∑
i∈Ij∩Iℓ
(
1
|Ij ∪ Iℓ|−
1
|Ij |−
1
|Iℓ|
)
(for j 6= ℓ)
Then we can verify that:
ft(S) = q(S) if at most two subsets overlap
ft(S) ≥ q(S) otherwise (overhestimated penalty)
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Previous and related work g
Unconstrained 0-1 Hyperbolic Programming
Single-ratio: NP-hard, poly with positive denominator (Hammer and Rudeanu 68)
Multiple-ratio: NP-hard; tackled by SA, Tabu, and decomposing into independent
polynomial single-ratio problems (Hansen, Poggi de Aragao and Ribeiro 90/91)
Constrained 0-1 Hyperbolic Programming
Single-ratio (Stancu-Minasian 97)
Multiple-ratio: MILP convex reformulations (Tawarmalani, Ahmed and Sahinidis 02)
Quadratic Set Covering Problem
Various application oriented works (Bazaara 75, Boros, Hammer et al. 00, ...)
Generic: not2p(|I|)-approximable for any polynomialp() (Escoffier and
Convex: approximable withinO(ln2(|I|)) but not withinρ ln2(|I|) Hammer 05)
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Complexity and Approximability (TCSP) g
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Complexity and Approximability (TCSP) g
Generic instances
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Complexity and Approximability (TCSP) g
Generic instances
Strongly NP-hard (Amaldi et al. 04)
Not approximable withinρ (√
|I|)1−ε or ρ (√
|J |)1−ε for a givenρ > 0
and anyε > 0, unless NP= ZPPReduction from Max Independent Set
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Complexity and Approximability (TCSP) g
Generic instances
Strongly NP-hard (Amaldi et al. 04)
Not approximable withinρ (√
|I|)1−ε or ρ (√
|J |)1−ε for a givenρ > 0
and anyε > 0, unless NP= ZPPReduction from Max Independent Set
Euclidean 2D Instances
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Complexity and Approximability (TCSP) g
Generic instances
Strongly NP-hard (Amaldi et al. 04)
Not approximable withinρ (√
|I|)1−ε or ρ (√
|J |)1−ε for a givenρ > 0
and anyε > 0, unless NP= ZPPReduction from Max Independent Set
Euclidean 2D Instances
Strongly NP-hard (does not admit a FPTAS unless P= NP)Adapting and extending a reduction for Disc-Cover (Fowler et al. 81)
Under a reasonable restriction, admits a PTASUsing the shifting lemma
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Complexity and Approximability (TCSP) g
Generic instances
Strongly NP-hard (Amaldi et al. 04)
Not approximable withinρ (√
|I|)1−ε or ρ (√
|J |)1−ε for a givenρ > 0
and anyε > 0, unless NP= ZPPReduction from Max Independent Set
Euclidean 2D Instances
Strongly NP-hard (does not admit a FPTAS unless P= NP)Adapting and extending a reduction for Disc-Cover (Fowler et al. 81)
Under a reasonable restriction, admits a PTASUsing the shifting lemma
Euclidean 1D Instances (or instances with C1C covering matrix)
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Complexity and Approximability (TCSP) g
Generic instances
Strongly NP-hard (Amaldi et al. 04)
Not approximable withinρ (√
|I|)1−ε or ρ (√
|J |)1−ε for a givenρ > 0
and anyε > 0, unless NP= ZPPReduction from Max Independent Set
Euclidean 2D Instances
Strongly NP-hard (does not admit a FPTAS unless P= NP)Adapting and extending a reduction for Disc-Cover (Fowler et al. 81)
Under a reasonable restriction, admits a PTASUsing the shifting lemma
Euclidean 1D Instances (or instances with C1C covering matrix)
Polynomial-time solvableLongest path on an appropriate directed acyclic digraph
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Complexity and Approximability (MCSP) g
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Complexity and Approximability (MCSP) g
Generic instances
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Complexity and Approximability (MCSP) g
Generic instances
Strongly NP-hard (Amaldi et al. 04)
Polynomial-time solvable if|Ij | = 2
Reduction to perfect b-matching
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Complexity and Approximability (MCSP) g
Generic instances
Strongly NP-hard (Amaldi et al. 04)
Polynomial-time solvable if|Ij | = 2
Reduction to perfect b-matching
Euclidean 2D Instances
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Complexity and Approximability (MCSP) g
Generic instances
Strongly NP-hard (Amaldi et al. 04)
Polynomial-time solvable if|Ij | = 2
Reduction to perfect b-matching
Euclidean 2D Instances
Strongly NP-hard (does not admit a FPTAS unless P= NP)Adapting the reduction for TCSP
Not approximable within3/2 unless P= NPConsequence of the above reduction
Under a reasonable restriction, approximable within a factor 3
Tiling with hexagons
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Linearization g
For each ratio1
1 +∑
h 6=i
yih
is introduced a variableri ≥ 0 and the quadratic constraint
ri =1
1 +∑
h 6=i
yih
≡ ri +∑
h 6=i
riyih = 1
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Linearization g
For each ratio1
1 +∑
h 6=i
yih
is introduced a variableri ≥ 0 and the quadratic constraint
ri =1
1 +∑
h 6=i
yih
≡ ri +∑
h 6=i
riyih = 1
ri · yih is standardly linearized with a variablezih ≥ 0 and the constraints
zih ≤ uiyih
zih ≥ liyih
zih ≥ ri + ui(yih − 1)
zih ≤ ri + li(yih − 1)
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Linearization g
For each ratio1
1 +∑
h 6=i
yih
is introduced a variableri ≥ 0 and the quadratic constraint
ri =1
1 +∑
h 6=i
yih
≡ ri +∑
h 6=i
riyih = 1
ri · yih is standardly linearized with a variablezih ≥ 0 and the constraints
zih ≤ uiyih
zih ≥ liyih
zih ≥ ri + ui(yih − 1)
zih ≤ ri + li(yih − 1)
NB: ri is continuous and bounded, andy is binary
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Tightening linearization of bilinear terms g
Z = {(r, y, z) : z = r · y, r ∈ [l, u], y ∈ {0, 1}}
conv(Z) =
{
z ≥ ly, z ≥ r + u(y − 1),
z ≤ uy, z ≤ r + l(y − 1)
}
1
0
yz
r
l
u
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Tightening linearization of bilinear terms g
Z = {(r, y, z) : z = r · y, r ∈ [l, u], y ∈ {0, 1}}
conv(Z) =
{
z ≥ ly, z ≥ r + u(y − 1),
z ≤ uy, z ≤ r + l(y − 1)
}
1
0
yz
r
l
u
Z = ∪ {(r, y, z) : z = 0, r ∈ [l , u ], y = 0}
Z ′ =∪ {(r, y, z) : z = r, r ∈ [l , u ], y = 1}
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Tightening linearization of bilinear terms g
Z = {(r, y, z) : z = r · y, r ∈ [l, u], y ∈ {0, 1}}
conv(Z) =
{
z ≥ ly, z ≥ r + u(y − 1),
z ≤ uy, z ≤ r + l(y − 1)
}
1
0
yz
r
l
u
Z ′ = ∪ {(r, y, z) : z = 0, r ∈ [l0, u0], y = 0}
Z ′ =∪ {(r, y, z) : z = r, r ∈ [l1, u1], y = 1}
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Tightening linearization of bilinear terms g
Z = {(r, y, z) : z = r · y, r ∈ [l, u], y ∈ {0, 1}}
conv(Z) =
{
z ≥ ly, z ≥ r + u(y − 1),
z ≤ uy, z ≤ r + l(y − 1)
}
1
0
yz
r
l
u
Z ′ = ∪ {(r, y, z) : z = 0, r ∈ [l0, u0], y = 0}
Z ′ =∪ {(r, y, z) : z = r, r ∈ [l1, u1], y = 1}
conv(Z ′) =
{
z ≥ l1y, z ≥ r + u0(y − 1),
z ≤ u1y, z ≤ r + l0(y − 1)
}
1
0
yz
r
l0
l1
u0
u1
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Lagrangean relaxation g
By applying Lagragean relaxation to an appropriate reformulation
the problem is decomposed intosmallerandeasiersubproblems.
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Lagrangean relaxation g
By applying Lagragean relaxation to an appropriate reformulation
the problem is decomposed intosmallerandeasiersubproblems.
Expanded formulation obtained by adding for eachi ∈ I a vector
χi = {χij : j ∈ Ji} of binary variables, one for each covering subset.
Incidence vector of alocal covering solutionfor i.
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Lagrangean relaxation g
By applying Lagragean relaxation to an appropriate reformulation
the problem is decomposed intosmallerandeasiersubproblems.
Expanded formulation obtained by adding for eachi ∈ I a vector
χi = {χij : j ∈ Ji} of binary variables, one for each covering subset.
Incidence vector of alocal covering solutionfor i.
i
Ji
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Lagrangean relaxation g
By applying Lagragean relaxation to an appropriate reformulation
the problem is decomposed intosmallerandeasiersubproblems.
Expanded formulation obtained by adding for eachi ∈ I a vector
χi = {χij : j ∈ Ji} of binary variables, one for each covering subset.
Incidence vector of alocal covering solutionfor i.
i
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Lagrangean relaxation g
Expanded formulation:
maxX
i∈I
1
1 +P
h∈Ni
yih
s.t.X
j∈Ji
xj ≥ 1 i ∈ I (1)
yih ≥ xj i ∈ I, h ∈ Ni, j ∈ Ji ∩ Jh (2)
X
j∈Ji
χij ≥ 1 i ∈ I (3)
yih ≥ χij i ∈ I, h ∈ Ni, j ∈ Ji ∩ Jh (4)
yih ≤X
j∈Ji∩Jh
χij i ∈ I, h ∈ Ni (5)
xj = χij i ∈ I, j ∈ Ji (6)
yih = yhi i ∈ I, h ∈ Ni : h > i (7)
xj , χij , yih ∈ {0, 1}
Several possibilities, depending on which constraints aredeleted/dualized
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Lagrangean relaxation g
Expanded formulation:
maxX
i∈I
1
1 +P
h∈Ni
yih
s.t.X
j∈Ji
xj ≥ 1 i ∈ I (1)
yih ≥ xj i ∈ I, h ∈ Ni, j ∈ Ji ∩ Jh (2)
X
j∈Ji
χij ≥ 1 i ∈ I (3)
yih ≥ χij i ∈ I, h ∈ Ni, j ∈ Ji ∩ Jh (4)
yih ≤X
j∈Ji∩Jh
χij i ∈ I, h ∈ Ni (5)
xj = χij i ∈ I, j ∈ Ji (6)
yih = yhi i ∈ I, h ∈ Ni : h > i (7)
xj , χij , yih ∈ {0, 1}
Several possibilities, depending on which constraints aredeleted/dualized
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Lagrangean relaxation g
Expanded formulation:
maxX
i∈I
1
1 +P
h∈Ni
yih
s.t.X
j∈Ji
xj ≥ 1 i ∈ I (1)
yih ≥ xj i ∈ I, h ∈ Ni, j ∈ Ji ∩ Jh (2)
X
j∈Ji
χij ≥ 1 i ∈ I (3)
yih ≥ χij i ∈ I, h ∈ Ni, j ∈ Ji ∩ Jh (4)
yih ≤X
j∈Ji∩Jh
χij i ∈ I, h ∈ Ni (5)
xj = χij i ∈ I, j ∈ Ji (6)
yih = yhi i ∈ I, h ∈ Ni : h > i (7)
xj , χij , yih ∈ {0, 1}
Without (2), (6) and (7): one SCP and|I| independent hyperbolic subproblems
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Lagrangean relaxation g
Expanded formulation:
maxX
i∈I
1
1 +P
h∈Ni
yih
s.t.X
j∈Ji
xj ≥ 1 i ∈ I (1)
yih ≥ xj i ∈ I, h ∈ Ni, j ∈ Ji ∩ Jh (2)
X
j∈Ji
χij ≥ 1 i ∈ I (3)
yih ≥ χij i ∈ I, h ∈ Ni, j ∈ Ji ∩ Jh (4)
yih ≤X
j∈Ji∩Jh
χij i ∈ I, h ∈ Ni (5)
xj = χij i ∈ I, j ∈ Ji (6)
yih = yhi i ∈ I, h ∈ Ni : h > i (7)
xj , χij , yih ∈ {0, 1}
LAGa: remove (2) and dualize (6) and (7)→ NP-hard hyperbolic subproblems
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Lagrangean relaxation g
Expanded formulation:
maxX
i∈I
1
1 +P
h∈Ni
yih
s.t.X
j∈Ji
xj ≥ 1 i ∈ I (1)
yih ≥ xj i ∈ I, h ∈ Ni, j ∈ Ji ∩ Jh (2)
X
j∈Ji
χij ≥ 1 i ∈ I (3)
yih ≥ χij i ∈ I, h ∈ Ni, j ∈ Ji ∩ Jh (4)
yih ≤X
j∈Ji∩Jh
χij i ∈ I, h ∈ Ni (5)
xj = χij i ∈ I, j ∈ Ji (6)
yih = yhi i ∈ I, h ∈ Ni : h > i (7)
xj , χij , yih ∈ {0, 1}
LAGb: remove (5), (6) and dualize (2), (7)→ polynomial hyperbolic subproblems
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Lagrangean subproblem for LAGb g
Problem for a given elementi:
max1
1 +P
h∈Ni
yh
+
X
h∈Ni
chyh
s.t.X
j∈Ji
χj ≥ 1
yh ≥ χj h ∈ Ni, j ∈ Ji ∩ Jh
χj ∈ {0, 1} j ∈ Ji
yh ∈ {0, 1} h ∈ Ni
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Lagrangean subproblem for LAGb g
Problem for a given elementi:
max1
1 +P
h∈Ni
yh
+
X
h∈Ni
chyh
s.t.X
j∈Ji
χj ≥ 1
yh ≥ χj h ∈ Ni, j ∈ Ji ∩ Jh
χj ∈ {0, 1} j ∈ Ji
yh ∈ {0, 1} h ∈ Ni
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Lagrangean subproblem for LAGb g
Fix one variableχℓ to 1 (try all). This covers allh ∈ Iℓ.
max1
1 +P
h∈Ni
yh
+
X
h∈Ni
chyh
s.t.X
j∈Ji
χj ≥ 1
yh ≥ χj h ∈ Ni, j ∈ Ji ∩ Jh
χj ∈ {0, 1} j ∈ Ji
yh ∈ {0, 1} h ∈ Ni
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Lagrangean subproblem for LAGb g
Fix one variableχℓ to 1 (try all). This covers allh ∈ Iℓ.
max1
1 +P
h∈Ni
yh
+
X
h∈Ni
chyh
s.t. χℓ = 1
yh ≥ χj h ∈ Ni, j ∈ Ji ∩ Jh
χj ∈ {0, 1} j ∈ Ji
yh ∈ {0, 1} h ∈ Ni
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Lagrangean subproblem for LAGb g
Fix one variableχℓ to 1 (try all). This covers allh ∈ Iℓ.
max1
1 +P
h∈Ni
yh
+
X
h∈Ni
chyh
s.t. χℓ = 1
yh = 1 h ∈ Iℓ
yh ≥ χj h ∈ Ni \ Iℓ, j ∈ Ji ∩ Jh
χj ∈ {0, 1} j ∈ Ji
yh ∈ {0, 1} h ∈ Ni
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Lagrangean subproblem for LAGb g
Fix all otherχj to 0 (no o.f. contribution).
max1
1 +P
h∈Ni
yh
+
X
h∈Ni
chyh
s.t. χℓ = 1
yh = 1 h ∈ Iℓ
yh ≥ χj h ∈ Ni \ Iℓ, j ∈ Ji ∩ Jh
χj ∈ {0, 1} j ∈ Ji
yh ∈ {0, 1} h ∈ Ni
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Lagrangean subproblem for LAGb g
Fix all otherχj to 0 (no o.f. contribution).
max1
1 +P
h∈Ni
yh
+
X
h∈Ni
chyh
s.t. yh = 1 h ∈ Iℓ
yh ∈ {0, 1} h ∈ Ni
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Lagrangean subproblem for LAGb g
Remains an unconstrained problem with hyperbolic+linear o.f..
max1
1 +P
h∈Ni
yh
+
X
h∈Ni
chyh
s.t. yh = 1 h ∈ Iℓ
yh ∈ {0, 1} h ∈ Ni
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Lagrangean subproblem for LAGb g
Remains an unconstrained problem with hyperbolic+linear o.f..
max1
1 +P
h∈Ni
yh
+
X
h∈Ni
chyh
s.t. yh = 1 h ∈ Iℓ
yh ∈ {0, 1} h ∈ Ni
Since hyperbolic depends only onhow manyand not onwhich:
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Lagrangean subproblem for LAGb g
Remains an unconstrained problem with hyperbolic+linear o.f..
max1
1 +P
h∈Ni
yh
+
X
h∈Ni
chyh
s.t. yh = 1 h ∈ Iℓ
yh ∈ {0, 1} h ∈ Ni
Since hyperbolic depends only onhow manyand not onwhich:
1) sortch coefficients in nonincreasing order. f
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Lagrangean subproblem for LAGb g
Remains an unconstrained problem with hyperbolic+linear o.f..
max1
1 +P
h∈Ni
yh
+
X
h∈Ni
chyh
s.t. yh = 1 h ∈ Iℓ
yh ∈ {0, 1} h ∈ Ni
Since hyperbolic depends only onhow manyand not onwhich:
1) sortch coefficients in nonincreasing order. f
2) fix the firstk variables to 1, the remaining to0 (try all k).
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Comparison - our department g
Our Department
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Comparison - our department g
Our Department
TCSP best solution
Standard Linearization Improved Linearization LAGb
|J| |I| den gap time gap time gap time
(%) (sec) (%) (sec) (%) (sec)
81 84 13.79.28 − 5.08 − 0.87 237.2
− : time limit exceeded
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Comparison - our department g
Our Department
TCSP best solution
SCP optimal solution
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Comparison - our department g
Our Department
TCSP best solution
SCP optimal solution
Tests with a WLAN simulator (ns-2):
2.58 Mb/s for SCP solution,15.8 Mb/s for TCSP solution
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Comparison - synthetic instances g
Standard Linearization Improved Linearization LAGb
|J| |I| den gap stdev time stdev gap stdev time stdev gap stdev time stdev
GEOMETRIC INSTANCES(LOW DENSITY)50 50 6.6 ∗ 0.4 0.3 ∗ 0.1 0.1 ∗ 0.5 0.350 100 6.4 ∗ 7.2 4.1 ∗ 4.1 4.1 0.11 0.15 5.3 2.8
100 100 5.3 0.79 1.51 1826.61639.3 ∗ 177.1 203.1 0.28 0.28 24.8 13.6100 200 5.1 9.42 2.57 − 3.07 1.88 3363.0530.0 0.37 0.22 409.6 129.550 300 6.3 ∗ 561.6 557.5 ∗ 395.3 353.9 ∗ 621.8 137.9
GEOMETRIC INSTANCES(HIGH DENSITY)50 50 10.5 ∗ 15.5 20.3 ∗ 6.1 5.7 0.17 0.32 2.0 1.750 100 10.3 ∗ 798.6 452.7 ∗ 313.6 188.9 0.10 0.14 52.5 29.8
100 100 10.8 27.76 3.42 − 12.26 3.43 − 1.89 0.61 215.0 24.8100 200 10.6 33.17 3.50 − 18.96 1.08 − 2.26 1.14 1111.2 44.550 300 11.1 27.12 7.28 − 26.43 6.69 − 0.98 0.69 1494.4140.7
STANDARD SCPINSTANCES (CLASS SCP4*)1000 200 2.0 11.53 1.69 − 6.13 1.65 − 0.12 0.09 3304.6403.6
STANDARD SCPINSTANCES (CLASS SCPE*)500 50 20.0 71.22 4.69 − 35.75 16.62 − 6.14 0.78 1765.9148.1
∗ : the primal-dual gap is zero (proven optimality)− : time limit exceeded for all instances of the class
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Concluding remarks g
This presentation:
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Concluding remarks g
This presentation:
New interesting class: set covering problems withcompeting ground-set elements
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Concluding remarks g
This presentation:
New interesting class: set covering problems withcompeting ground-set elements
Complexity and approximability for generic and geometric versions
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Concluding remarks g
This presentation:
New interesting class: set covering problems withcompeting ground-set elements
Complexity and approximability for generic and geometric versions
Improved linearization and efficient Lagrangean relaxation
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Concluding remarks g
This presentation:
New interesting class: set covering problems withcompeting ground-set elements
Complexity and approximability for generic and geometric versions
Improved linearization and efficient Lagrangean relaxation
Ongoing work:
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Concluding remarks g
This presentation:
New interesting class: set covering problems withcompeting ground-set elements
Complexity and approximability for generic and geometric versions
Improved linearization and efficient Lagrangean relaxation
Ongoing work:
Linearization byDantzig-Wolfedecomposition
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Concluding remarks g
This presentation:
New interesting class: set covering problems withcompeting ground-set elements
Complexity and approximability for generic and geometric versions
Improved linearization and efficient Lagrangean relaxation
Ongoing work:
Linearization byDantzig-Wolfedecomposition
Refined hyperbolic models, accounting for relevant features of WLANs
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Concluding remarks g
This presentation:
New interesting class: set covering problems withcompeting ground-set elements
Complexity and approximability for generic and geometric versions
Improved linearization and efficient Lagrangean relaxation
Ongoing work:
Linearization byDantzig-Wolfedecomposition
Refined hyperbolic models, accounting for relevant features of WLANs
Direct interference and node association
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Concluding remarks g
This presentation:
New interesting class: set covering problems withcompeting ground-set elements
Complexity and approximability for generic and geometric versions
Improved linearization and efficient Lagrangean relaxation
Ongoing work:
Linearization byDantzig-Wolfedecomposition
Refined hyperbolic models, accounting for relevant features of WLANs
Direct interference and node association
Multiple frequenciesandadaptive rate
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”
Concluding remarks g
This presentation:
New interesting class: set covering problems withcompeting ground-set elements
Complexity and approximability for generic and geometric versions
Improved linearization and efficient Lagrangean relaxation
Ongoing work:
Linearization byDantzig-Wolfedecomposition
Refined hyperbolic models, accounting for relevant features of WLANs
Direct interference and node association
Multiple frequenciesandadaptive rate
Sandro Bosio, AUSSOIS 2007, “Hyperbolic set covering problems with competing ground-set elements”