case studies: bin packing & the traveling salesman problem
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Case Studies: Bin Packing & The Traveling Salesman Problem. Bin Packing: Part II. David S. Johnson AT&T Labs – Research. Asymptotic Worst-Case Ratios. Theorem: R ∞ (FF) = R ∞ (BF) = 17/10 . Theorem: R ∞ (FFD) = R ∞ (BFD) = 11/9. Average-Case Performance. Progress?. - PowerPoint PPT PresentationTRANSCRIPT
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Case Studies: Bin Packing &
The Traveling Salesman Problem
David S. JohnsonAT&T Labs – Research
Bin Packing: Part II
Asymptotic Worst-Case Ratios
• Theorem: R∞(FF) = R∞(BF) = 17/10.
• Theorem: R∞(FFD) = R∞(BFD) = 11/9.
Average-Case Performance
Progress?
Progress:Faster Computers Bigger Instances
Definitions
Definitions, Continued
Theorems for U[0,1]
Proof Idea for FF, BF:View as a 2-Dimensional Matching
Problem
Distributions U[0,u]
Item sizes uniformly distributed in the interval (0,u], 0 < u < 1
Average Waste for BF under U(0,u]
Measured Average Waste for BF under U(0,.01]
Conjecture
FFD on U(0,u]
Experimental Results from [Bentley, Johnson, Leighton, McGeoch, 1983]
N =
FFD
(L)
– s(
L)
u = .6
u = .5
u = .4
FFD on U(0,u], u 0.5
FFD on U(0,u], u 0.5
FFD on U(0,u], 0.5 u 1
1984 – 2011?)
Discrete Distributions
Courcoubetis-Weber
y
x
z
(0,0,0)
(2,1,1)
(0,2,1)
(1,0,2)
Courcoubetis-Weber Theorem
A Flow-Based Linear Program
Theorem [Csirik et al. 2000]
Note: The LP’s for (1) and (3) are both of size polynomial in B, not log(B), and hence “pseudo-polynomial”
0.25
0.00
0.75
0.50
1.00
1/3
1
2/3
Discrete Uniform Distributions
U{3,4}U{6,8}U{12,16}U(0,¾]
Theorem [Coffman et al. 1997]
(Results analogous to those for the corresponding U(0,u])
Experimental Results for Best Fit
0 ≤ u ≤ 1, 1 ≤ j ≤ k = 51
Averages of 25 trials for each distribution, N = 2,048,000
Average Waste under Best Fit(Experimental values for N = 100,000,000 and
200,000,000)
[GJSW, 1993]
Linear Waste
Average Waste under Best Fit(Experimental values for N = 100,000,000 and
200,000,000)
[GJSW, 1993][KRS, 1996]Holds for all j = k-2
Average Waste under Best Fit(Experimental values for N = 100,000,000 and
200,000,000)
[GJSW, 1993]
Still Open
Theorem [Kenyon & Mitzenmacher, 2000]
Average wBF(L)/s(L) for U{j,85}
Average wBFD(L)/s(L) for U{j,85}
Averages on the Same Scale
The Discrete Distribution U{6,13}
“Fluid Algorithm” Analysis: U{6,13}
Size = 6 5 4 3 2 1
Amount = β β β β β β
Bin Type =
Amount =
6
6
β/2
β/2β/2
4
4
4
β/3
β/6
β/2
5
5
33
3
3
3
β/8
β/24
22
222
2
β/24
¾β
Expected Waste
Theorem[Coffman, Johnson, McGeoch, Shor, & Weber, 1994-
2011]
U{j,k} for which FFD has Linear Waste
j
k
Minumum j/k for which Waste is Linear
k
j/k
Values of j/k for which Waste is Maximum
k
j/k
Waste as a Function of j and k (mod 6)
K = 8641 = 26335 + 1
Pairs (j,k) where BFD beats FFD
k
j
Pairs (j,k) where FFD beats BFD
k
j
Beating BF and BFD in Theory
Plausible Alternative Approach
The Sum-of-Squares Algorithm (SS)
SS on U{j,100} for 1 ≤ j ≤ 99
j
SS(L
)/s(
L)
BF for N = 10M
SS for N = 1M
SS for N = 100K
SS for N = 10M
Discrete Uniform Distributions II
j
h
K = 101
j
h
K = 120
j
h
j
h
K = 100
h = 18
Results for U{18..j,k}
j
A(L
)/s(
L)
BFSSOPT
Is SS Really this Good?
Conjectures [Csirik et al., 1998]
Why O(log n) Waste?
Theorem [Csirik et al., 2000]
Proving the Conjectures: A Key Lemma
Linear Waste Distributions
Good News
SSF for U{18.. j,100}
Handling Unknown Distributions
SS* for U{18.. j,100}
Other Exponents
Variants that Don’t Always Work
Offline Packing Revisited:
The Cutting-Stock Problem
Gilmore-Gomory vs Bin Packing Heuristics
Some Remaining Open Problems