linear and integer programming: an...
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Martin Grötschel Institut für Mathematik, Technische Universität Berlin (TUB)DFG-Forschungszentrum “Mathematik für Schlüsseltechnologien” (MATHEON)Konrad-Zuse-Zentrum für Informationstechnik Berlin (ZIB)
[email protected] http://www.zib.de/groetschel
01M1 LectureLinear and Integer Programming:
an Introduction
Martin Grötschel Block Course at TU Berlin
"Combinatorial Optimization at Work“
October 4 – 15, 2005
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MartinGrötschel
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CO atWork Contents
1. Linear, integer, nonlinear programming, optimization: What‘s that?2. Historic roots3. LP-Theory4. Algorithms for the solution of linear programs
1) Fourier-Motzkin Elimination2) The Simplex Method3) The Ellipsoid Method4) Interior-Point/Barrier Methods
5. Algorithms for the solution of integer programs1) Branch&Bound2) Cutting Planes
6. Where are we today? 1) State of the art in LP2) State of the art in IP3) Examples
will be covered by Bob Bixbyon Saturday
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MartinGrötschel
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CO atWork Contents
1. Linear, integer, nonlinear programming, optimization: What‘s that?2. Historic roots3. LP-Theory4. Algorithms for the solution of linear programs
1) Fourier-Motzkin Elimination2) The Simplex Method3) The Ellipsoid Method4) Interior-Point/Barrier Methods
5. Algorithms for the solution of integer programs1) Branch&Bound2) Cutting Planes
6. Where are we today? 1) State of the art in LP2) State of the art in IP3) Examples
will be covered by Bob Bixbyon Saturday
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MartinGrötschel
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CO atWork typical optimization problems
max ( ) min ( )( ) 0, 1,2,...,( ) 0, 1,2,...,
( )
i
j
n
f x or f xg x i kh x j m
x and x S
= =≤ =
∈ ∈R ( )
( )
min
0n
n
T
x
x
c xAx aBx b
x
∈
∈
=≤≥
n
n
R
k { }
min
0
( 0,1 )
T
n
n
c xAx aBx b
xx
x
=≤≥
∈
∈
Z
linearprogram
LP
(linear)integer
programIP, MIP
„general“(nonlinear)program
NLP
program = optimization problem
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MartinGrötschel
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CO atWork Contents
1. Linear, integer, nonlinear programming, optimization: What‘s that?2. Historic roots3. LP-Theory4. Algorithms for the solution of linear programs
1) Fourier-Motzkin Elimination2) The Simplex Method3) The Ellipsoid Method4) Interior-Point/Barrier Methods
5. Algorithms for the solution of integer programs1) Branch&Bound2) Cutting Planes
6. Where are we today? 1) State of the art in LP2) State of the art in IP3) Examples
will be covered by Bob Bixbyon Saturday
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MartinGrötschel
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CO atWork Linear Programming
0
Tc xAx bx=≥
max 1 1 2 2
11 1 12 2 1 1
21 1 22 2 2 2
1 1 2 2
1 2
...
...
.......
, ,..., 0
n n
n n
n n
m m mn n m
n
c x c x c xsubject to
a x a x a x ba x a x a x b
a x a x a x bx x x
+ + +
+ + + =
+ + + =
+ + + =≥
max
linear programin standard form
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CO atWork Linear Programming
1939 L. V. Kantorovitch: Foundations of linear programming (Nobel Prize 1975)
1947 G. B. Dantzig: Invention of the simplex algorithm
Today: In my opinion and from an economic point of view, linear programming is the most important development of mathematics in the 20th century.
0
Tc xAx bx=≥
max
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Optimal use of scarce ressourcesfoundation and economic interpretation of LP
Leonid V. Kantorovich Tjalling C. KoopmansNobel Prize for Economics 1975
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Stiglers „Diet Problem“:„The first linear program“
Min x1 + x2
2x1 + x2 ≥ 3
x1 + 2x2 ≥ 3
x1 ≥ 0
x2 ≥ 0
costs
protein
carbohydrates
potatoes
beans
minimizing thecost of food
George J. StiglerNobel Prize in economics 1982
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CO atWork Diet Problem
Sets n nutrients / calorie thousands , protein grams , calcium grams , iron milligrams vitamin-a thousand ius, vitamin-b1 milligrams, vitamin-b2 milligrams, niacin milligrams , vitamin-c milligrams /
f foods / wheat , cornmeal , cannedmilk, margarine , cheese , peanut-b , lard liver , porkroast, salmon , greenbeans, cabbage , onions , potatoes spinach, sweet-pot, peaches , prunes , limabeans, navybeans / Parameter b(n) required daily allowances of nutrients / calorie 3, protein 70 , calcium .8 , iron 12 vitamin-a 5, vitamin-b1 1.8, vitamin-b2 2.7, niacin 18, vitamin-c 75 / Table a(f,n) nutritive value of foods (per dollar spent)
calorie protein calcium iron vitamin-a vitamin-b1 vitamin-b2 niacin vitamin-c (1000) (g) (g) (mg) (1000iu) (mg) (mg) (mg) (mg)
wheat 44.7 1411 2.0 365 55.4 33.3 441 cornmeal 36 897 1.7 99 30.9 17.4 7.9 106 cannedmilk 8.4 422 15.1 9 26 3 23.5 11 60 margarine 20.6 17 .6 6 55.8 .2 cheese 7.4 448 16.4 19 28.1 .8 10.3 4 peanut-b 15.7 661 1 48 9.6 8.1 471 lard 41.7 .2 .5 5 liver 2.2 333 .2 139 169.2 6.4 50.8 316 525 porkroast 4.4 249 .3 37 18.2 3.6 79 salmon 5.8 705 6.8 45 3.5 1 4.9 209 greenbeans 2.4 138 3.7 80 69 4.3 5.8 37 862 cabbage 2.6 125 4 36 7.2 9 4.5 26 5369 onions 5.8 166 3.8 59 16.6 4.7 5.9 21 1184 potatoes 14.3 336 1.8 118 6.7 29.4 7.1 198 2522 spinach 1.1 106 138 918.4 5.7 13.8 33 2755 sweet-pot 9.6 138 2.7 54 290.7 8.4 5.4 83 1912 peaches 8.5 87 1.7 173 86.8 1.2 4.3 55 57 prunes 12.8 99 2.5 154 85.7 3.9 4.3 65 257 limabeans 17.4 1055 3.7 459 5.1 26.9 38.2 93 navybeans 26.9 1691 11.4 792 38.4 24.6 217 Positive Variable x(f) dollars of food f to be purchased daily (dollars) Free Variable cost total food bill (dollars) Equations nb(n) nutrient balance (units), cb cost balance (dollars) ; nb(n).. sum(f, a(f,n)*x(f)) =g= b(n); cb.. cost=e= sum(f, x(f)); Model diet stiglers diet problem / nb,cb /;
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Goal: find the cheapest combination of foods that will satisfy the daily requirements of a person
motivated by the army’s desire to meet nutritional requirements of the soldiers at minimum cost
Army’s problem had 77 unknowns and 9 constraints.Stigler solved problem using a heuristic: $39.93/year (1939)Laderman (1947) used simplex: $39.69/year (1939 prices)
first “large-scale computation”took 120 man days on hand operated desk calculators (10 human “computers”)
http://www.mcs.anl.gov/home/otc/Guide/CaseStudies/diet/index.html
Solution of the Diet Problem
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CO atWork Milton Friedman on George J. Stigler
An early example of the latter is an article on "The Cost of Subsistence" (1945), which starts, "Elaborate investigations have been made of the adequacy of dietsat various income levels, and a considerable number of 'low-cost,' 'moderate,' and 'expensive' diets have been recommended to consumers. Yet, so far as I know, no one has determined the minimum cost of obtaining the amounts of calories, proteins, minerals, and vitamins which these studies accept as adequateor optimum." George then set himself to determine the minimum cost diet, in theprocess producing one of the earliest formulations of a linear programmingproblem in economics, for which he found an approximate solution, explainingthat "there does not appear to be any direct method of finding the minimum of a linear function subject to linear constraints." Two years later George Dantzigprovided such a direct method, the simplex method, now widely used in manyeconomic and industrial applications.
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CO atWork George Dantzig and Ralph Gomory
„founding fathers“
~1950linear programming
~1960integer programming
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MartinGrötschel
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CO atWork George Dantzig and Ralph Gomory
the fathers of Linear Programming and Integer Programming
ISMP Atlanta 2000
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CO atWork Dantzig and Bixby
George Dantzig and Bob Bixbyat the International Symposium on Mathematical Programming,
Atlanta, August 2000
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1954, the Beginning of IPG. Dantzig, D.R. Fulkerson, S. Johnson
USA49 cities
1146 variables
1954
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CO atWork Commercial software
William Orchard-Hayes (in the period 1953-1954)
The first commercial LP-Code was on the market in 1954 (i.e., ~50 years ago) and available on an IBM CPC (card programmable calculator):
Code: Simplex Algorithm with explicit basis inverse, that was recomputed in each step.
Shortly after, Orchard-Hayes implemented a version with product form of the inverse (idea of A. Orden),Record: 71 variables, 26 constraints, 8 h running time
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CO atWork Contents
1. Linear, integer, nonlinear programming, optimization: What‘s that?2. Historic roots3. LP-Theory4. Algorithms for the solution of linear programs
1) Fourier-Motzkin Elimination2) The Simplex Method3) The Ellipsoid Method4) Interior-Point/Barrier Methods
5. Algorithms for the solution of integer programs1) Branch&Bound2) Cutting Planes
6. Where are we today? 1) State of the art in LP2) State of the art in IP3) Examples
will be covered by Bob Bixbyon Saturday
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MartinGrötschel
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CO atWork Optimizers‘ dream: Duality theorems
Max-Flow Min-Cut TheoremThe maximal (s,t)-flow in a capacitated network is equal to theminimal capacity of an (s,t)-cut.
The Duality Theorem of linear programming
max
0
Tc xAx bx≤≥
min
0
T
T T
y by A c
y≥≥
=
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Optimizers‘ dream: Duality theorems for integer programming
The Max-Flow Min-Cut Theoremdoes not hold if several source-sink relations are given(multicommodity flow).
The Duality Theorem of linear programmingdoes not hold if integrality conditions are added
max
0
T
n
c xAx bxx
≤
∈
≥
Z
min
0
T
T
m
T
y by A c
yy
≥
∈
≥
Z
≤
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CO atWork Important theorems
complementary slackness theorems
redundancy characterizations
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MartinGrötschel
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CO atWork LP Solvability
Linear programs can be solved in polynomial time with
the Ellipsoid Method (Khachiyan, 1979)
Interior Points Methods (Karmarkar, 1984, and others)
Open: is there a strongly polynomial time algorithm for the solutionof LPs?
Certain variants of the Simplex Algorithm run – under certainconditions – in expected polynomial time (Borgwardt, 1977…)
Open: Is there a polynomial time variant of theSimplex Algorithm?
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CO atWork LP Solvability: Generalizations
Theorem (GLS 1979, 1988) (modulo technical details) :There exists a polynomial time algorithm to minimize convex functions(e.g., linear functions) over the elements of a class of convex bodies K(e. g. polyhedra) if and only if, there exists a polynomial time algorithmthat decides, for any given point x, whether x is in K, and that, whenx is not in K, finds a hyperplane that separates x from K.
Short version: Optimization and Separation are polynomial-timeequivalent.
Consequence: Theoretical Foundation of cutting plane algorithms.
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CO atWork Separation
K
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CO atWork IP Solvability
TheoremInteger, 0/1, and mixed integer programming are NP-hard.
Consequencespecial cases
special purposes
heuristics
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CO atWork Contents
1. Linear, integer, nonlinear programming, optimization: What‘s that?2. Historic roots3. LP-Theory4. Algorithms for the solution of linear programs
1) Fourier-Motzkin Elimination2) The Simplex Method3) The Ellipsoid Method4) Interior-Point/Barrier Methods
5. Algorithms for the solution of integer programs1) Branch&Bound2) Cutting Planes
6. Where are we today? 1) State of the art in LP2) State of the art in IP3) Examples
will be covered by Bob Bixbyon Saturday
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CO atWork
Iterative methods that solve the equation and inequality sytemsrepresenting the necessary local optimality conditions.
Sufficient conditions are rarely checked.
1
~ " "~" "
i i i i
i
i
x x dd descent direction
steplength
Algorithms for nonlinear programming
λ
λ
+ = +
( )i id f x= −∇ Steepest descent
1( ( )) ( )i i id H x f x−= − ∇ Newton
(Quasi-Newton, conjugate-gradient-, SQP-, subgradient…methods)
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CO atWork Contents
1. Linear, integer, nonlinear programming, optimization: What‘s that?2. Historic roots3. LP-Theory4. Algorithms for the solution of linear programs
1) Fourier-Motzkin Elimination2) The Simplex Method3) The Ellipsoid Method4) Interior-Point/Barrier Methods
5. Algorithms for the solution of integer programs1) Branch&Bound2) Cutting Planes
6. Where are we today? 1) State of the art in LP2) State of the art in IP3) Examples
will be covered by Bob Bixbyon Saturday
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CO atWork Fourier-Motzkin Elimination
Fourier, 1847
Motzkin, 1938
Method: successive projection of a polyhedron in n-dimensional space into a vector space of dimension n-1 byelimination of one variable.
Projection on y: (0,y)
Projection on x: (x,0)
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CO atWork A Fourier-Motzkin step
0
.
.
.
.
.
.
.
.
.
.
0
1
.
.
1
-1
.
.
.
.
-1
0
.
0
a1
al
am
b1
.
bk
0
.
0
â1
ân
b1
.bk
+
+
copy
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Fourier-Motzkin Elimination:an example
min/max + x1 + 3x2
(1) - x2 <= 0(2) - x1 - x2 <=-1(3) - x1 + x2 <= 3(4) + x1 <= 3(5) + x1 + 2x2 <= 9
(1)
(2)
(4)
(5)(3)
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CO atWork
Fourier-Motzkin Elimination:an example, call of PORTA
DIM = 3
INEQUALITIES_SECTION
(1) - x2 <= 0(2) - x1 - x2 <=-1(3) - x1 + x2 <= 3(4) + x1 <= 3(5) + x1 + 2x2 <= 9(6) + x1 + 3x2 - x3 <= 0(7) - x1 - 3x2 + x3 <= 0
ELIMINATION_ORDER1 0 0
min/max + x1 + 3x2
(1) - x2 <= 0(2) - x1 - x2 <=-1(3) - x1 + x2 <= 3(4) + x1 <= 3(5) + x1 + 2x2 <= 9
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CO atWork
Fourier-Motzkin Elimination:an example
DIM = 3
INEQUALITIES_SECTION
(1) - x2 <= 0(2) - x1 - x2 <=-1(3) - x1 + x2 <= 3(4) + x1 <= 3(5) + x1 + 2x2 <= 9(6) + x1 + 3x2 - x3 <= 0(7) - x1 - 3x2 + x3 <= 0
ELIMINATION_ORDER1 0 0
DIM = 3
INEQUALITIES_SECTION
(1) (1) - x2 <= 0(2,4) (2) - x2 <= 2(2,5) (3) + x2 <= 8(2,6) (4) +2x2 - x3 <= -1(3,4) (5) + x2 <= 6(3,5) (6) + x2 <= 4(3,6) (7) +4x2 - x3 <= 3(7,4) (8) -3x2 + x3 <= 3(7,5) (9) - x2 + x3 <= 9(7,6)
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Fourier-Motzkin Elimination:an example
(1,4) ( 1) -x3 <= -1(1,7) ( 2) -x3 <= 3(2,4) ( 3) -x3 <= 3(2,7) ( 4) -x3 <= 11(8,3) ( 5) +x3 <= 27(8,4) ( 6) -x3 <= 3(8,5) ( 7) +x3 <= 21(8,6) ( 8) +x3 <= 15(8,7) ( 9) +x3 <= 21(9,3) ( 10) +x3 <= 17(9,4) ( 11) +x3 <= 17(9,5) ( 12) +x3 <= 15(9,6) ( 13) +x3 <= 13(9,7) ( 14)+3x3 <= 39
min = 1 <= x3 <= 13 = max
x1 = 1 x1 = 1x2 = 0 x2 = 4
DIM = 3
INEQUALITIES_SECTION
(1) (1) - x2 <= 0(2,4) (2) - x2 <= 2(2,5) (3) + x2 <= 8(2,6) (4) +2x2 - x3 <= -1(3,4) (5) + x2 <= 6(3,5) (6) + x2 <= 4(3,6) (7) +4x2 - x3 <= 3(7,4) (8) -3x2 + x3 <= 3(7,5) (9) - x2 + x3 <= 9(7,6)
ELIMINATION_ORDER0 1 0
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Fourier-Motzkin Elimination:an example
min/max + x1 + 3x2
(1) - x2 <= 0(2) - x1 - x2 <=-1(3) - x1 + x2 <= 3(4) + x1 <= 3(5) + x1 + 2x2 <= 9
(1)
(2)
(4)
(5)(3)
max
min
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CO atWork Contents
1. Linear, integer, nonlinear programming, optimization: What‘s that?2. Historic roots3. LP-Theory4. Algorithms for the solution of linear programs
1) Fourier-Motzkin Elimination2) The Simplex Method3) The Ellipsoid Method4) Interior-Point/Barrier Methods
5. Algorithms for the solution of integer programs1) Branch&Bound2) Cutting Planes
6. Where are we today? 1) State of the art in LP2) State of the art in IP3) Examples
will be covered by Bob Bixbyon Saturday
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CO atWork The Simplex Method
Dantzig, 1947: primal Simplex Method
Lemke, 1954; Beale, 1954: dual Simplex Method
Dantzig, 1953: revised Simplex Method
….
Underlying Idea: Find a vertex of the set of feasible LP solutions (polyhedron) and move to a better neighbouringvertex, if possible.
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The Simplex Method:an example
min/max + x1 + 3x2
(1) - x2 <= 0(2) - x1 - x2 <=-1(3) - x1 + x2 <= 3(4) + x1 <= 3(5) + x1 + 2x2 <= 9
(1)
(2)
(4)
(5)(3)
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The Simplex Method:an example
min/max + x1 + 3x2
(1) - x2 <= 0(2) - x1 - x2 <=-1(3) - x1 + x2 <= 3(4) + x1 <= 3(5) + x1 + 2x2 <= 9
(1)
(2)
(4)
(5)(3)
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CO atWork Hirsch Conjecture
If P is a polytope of dimension n with m facets then everyvertex of P can be reached from any other vertex of P on a path of length at most m-n.In the example before: m=5, n=2 and m-n=3, conjecture is true.
At present, not even a polynomial bound on the path length is known.
Best upper bound: Kalai, Kleitman (1992): The diameter of the graph of an n-dimensional polyhedron with m facets is at most m(log n+1).
Lower bound: Holt, Klee (1997): at least m-n (m, n large enough).
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computationally important idea of theSimplex Method
0
Tc xAx bx=≥
max
Let a (m,n)-Matrix A with full row rank m, an m-vector b and an n-vector c with m<n be given. For every vertex y of thepolyhedron of feasible solutions of the LP,
there is a non-singular (m,m)-submatrix B (called basis) of A representing the vertex y (basic solution) as follows
1 , 0B Ny B b y−= =
Many computational consequences:Update-formulas, reduced cost calculations, number of non-zeros of a vertex,…
A = B N
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CO atWork Contents
1. Linear, integer, nonlinear programming, optimization: What‘s that?2. Historic roots3. LP-Theory4. Algorithms for the solution of linear programs
1) Fourier-Motzkin Elimination2) The Simplex Method3) The Ellipsoid Method4) Interior-Point/Barrier Methods
5. Algorithms for the solution of integer programs1) Branch&Bound2) Cutting Planes
6. Where are we today? 1) State of the art in LP2) State of the art in IP3) Examples
will be covered by Bob Bixbyon Saturday
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CO atWork The Ellipsoid Method
Shor, 1970 - 1979
Yudin & Nemirovskii, 1976
Khachiyan, 1979
M. Grötschel, L. Lovász, A. Schrijver, Geometric Algorithms and Combinatorial Optimization
Algorithms and Combinatorics 2, Springer, 1988
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CO atWork The Ellipsoid Method: an example
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TheEllipsoid Method
Initialization
Stopping criterionFeasibility checkCutting plane
choice
Update
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CO atWork Ellipsoid Method
feasiblesolutionfound
a(1)
a(0)
a(2)
a(7)
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CO atWork Contents
1. Linear, integer, nonlinear programming, optimization: What‘s that?2. Historic roots3. LP-Theory4. Algorithms for the solution of linear programs
1) Fourier-Motzkin Elimination2) The Simplex Method3) The Ellipsoid Method4) Interior-Point/Barrier Methods
5. Algorithms for the solution of integer programs1) Branch&Bound2) Cutting Planes
6. Where are we today? 1) State of the art in LP2) State of the art in IP3) Examples
will be covered by Bob Bixbyon Saturday
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CO atWork Interior-Point Methods: an example
(1)
(2)
(4)
(5)(3)
min
central path
interior Point
Often also calledBarrier Methods
Why?
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CO atWork Another approach
Lagrangean Relaxation(for very large scale and structured LPs)
plussubgradient
bundle
bundle trust region
or any other nondifferentiable NLP method that lookspromissing
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CO atWork Contents
1. Linear, integer, nonlinear programming, optimization: What‘s that?2. Historic roots3. LP-Theory4. Algorithms for the solution of linear programs
1) Fourier-Motzkin Elimination2) The Simplex Method3) The Ellipsoid Method4) Interior-Point/Barrier Methods
5. Algorithms for the solution of integer programs1) Branch&Bound2) Cutting Planes
6. Where are we today? 1) State of the art in LP2) State of the art in IP3) Examples
will be covered by Bob Bixbyon Saturday
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special „simple“combinatorial optimization problemsFinding a
minimum spanning tree
shortest path
maximum matching
maximal flow through a network
cost-minimal flow
…
solvable in polynomial time by special purpose algorithms
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special „hard“combinatorial optimization problems
travelling salesman problem
location und routing
set-packing, partitioning, -covering
max-cut
linear ordering
scheduling (with a few exceptions)
node and edge colouring
…
NP-hard (in the sense of complexity theory)
The most successful solution techniques employ linear programming.
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CO atWork Contents
1. Linear, integer, nonlinear programming, optimization: What‘s that?2. Historic roots3. LP-Theory4. Algorithms for the solution of linear programs
1) Fourier-Motzkin Elimination2) The Simplex Method3) The Ellipsoid Method4) Interior-Point/Barrier Methods
5. Algorithms for the solution of integer programs1) Branch&Bound2) Cutting Planes
6. Where are we today? 1) State of the art in LP2) State of the art in IP3) Examples
will be covered by Bob Bixbyon Saturday
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The Branch&Bound Technique:An Example
{ }
min
0
0,1
T
n
c xAx aBx b
x
x
=≤≥
∈
0/1-program
Solve the LP-relaxation and getoptimal solution y. (lower bound)If y integral, DONE!Otherwise pick fractional component y(i).Create two new subproblems byadding y(i)=1 and y(i)=0, resp.….
{ }1
min
0
0,1
T
n
c xAx aBx b
x
x
x
≤≥
∈
≤
=
LP-relaxation
y(i)=1y(i)=0
y(j)=1y(k)=1
integral solution= upper bound
LP solution= lower bound
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CO atWork Branching (in general)
Current solution is infeasible
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CO atWork Branching (in general)
Decomposition into subproblems removes infeasiblesolution
Rounding a fractional component up and down
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A BranchingTree
Applegate
Bixby
Chvátal
Cook
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CO atWork Contents
1. Linear, integer, nonlinear programming, optimization: What‘s that?2. Historic roots3. LP-Theory4. Algorithms for the solution of linear programs
1) Fourier-Motzkin Elimination2) The Simplex Method3) The Ellipsoid Method4) Interior-Point/Barrier Methods
5. Algorithms for the solution of integer programs1) Branch&Bound2) Cutting Planes
6. Where are we today? 1) State of the art in LP2) State of the art in IP3) Examples
will be covered by Bob Bixbyon Saturday
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cutting plane technique for integer and mixed-integer programming
Feasibleintegersolutions
LP-basedrelaxation
Convexhull
Objectivefunction
Cuttingplanes
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CO atWork Other Names
Branch & Cut
Branch & Price
Branch & Cut & Price
etc.
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CO atWork Contents
1. Linear, integer, nonlinear programming, optimization: What‘s that?2. Historic roots3. LP-Theory4. Algorithms for the solution of linear programs
1) Fourier-Motzkin Elimination2) The Simplex Method3) The Ellipsoid Method4) Interior-Point/Barrier Methods
5. Algorithms for the solution of integer programs1) Branch&Bound2) Cutting Planes
6. Where are we today?1) State of the art in LP2) State of the art in IP3) Examples
will be covered by Bob Bixbyon Saturday
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CO atWork The most recent LP survey
Robert E. Bixby, Solving Real-World Linear Programs: A Decade and Moreof Progress. Operations Research 50 (2002)3-15.
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Information about computational Mixed Integer Programming, see, e.g.,
This book appeared in MPS-SIAM "Series on Optimization", 2004, One particularly interesting article on MIP:
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Which LP solvers areused in practice?
Fourier-Motzkin: hopeless
Ellipsoid Method: total failure
primal Simplex Method: good
dual Simplex Method: better
Barrier Method: for LPs frequently even better
For LP relaxations of IPs: dual Simplex Method
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CO atWork Summary
We can solve today explicit LPs withup to 500,000 of variables and
up to 5,000,000 of constraints routinely
in relatively short running times.
We can solve today structured implicit LPs (employingcolumn generation and cutting plane techniques) in special cases with hundreds of million (and more) variables and almost infinitly many constraints in acceptable running times.(Examples: TSP, bus circulation in Berlin)
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CO atWork State of the art in LP and IP
This will be covered in the lectures of Bob BixbyOperations Research Management Science Today - June 2005
OR-MS Today - LINEAR PROGRAMMING SOFTWARE SURVEY
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Martin Grötschel Institut für Mathematik, Technische Universität Berlin (TUB)DFG-Forschungszentrum “Mathematik für Schlüsseltechnologien” (MATHEON)Konrad-Zuse-Zentrum für Informationstechnik Berlin (ZIB)
[email protected] http://www.zib.de/groetschel
01M1 LectureLinear and Integer Programming:
an Introduction
Martin Grötschel Block Course at TU Berlin
"Combinatorial Optimization at Work“
October 4 – 15, 2005 The End