- Meeting 27 : Wed, Feb 25, 12:00 pm-12:50 pm -
References | |
Exercises | |
Reading | |
Set Cover LP and f-approximation for weighted set cover
via deterministic rounding. Notion of dual. Exercises -- formulate VC, Knapsack as Linear Programs. Construct the duals.
References: | Chapter 12 of Vazirani. Chapter 1 of Shmoys and Williamsons.
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- Meeting 28 : Fri, Feb 27, 11:00 am-11:50 am -
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Exercises | |
Reading | |
More on Duality. Proof of Weak duality and statement of strong duality. Complementary slackness conditions. Examples and proof of one direction (if primal and dual solutions are optimal, then they satisfy complementary slackness).
References: | Chapter 12, Vazirani.
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- Meeting 29 : Mon, Mar 02, 11:00 am-11:50 am -
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Exercises | |
Reading | |
1/2 integrality of vertex cover. Linear programs with exponentially many constraints. Warm-up exercise s-t shortest paths. Prize Collecting Steiner Tree.
References: | Chapter 14 Vazirani (1/2 integrality of VC) and Chapter 4, Shmoys and Williamsons.
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- Meeting 30 : Tue, Mar 03, 08:00 am-08:50 am -
References | |
Exercises | |
Reading | |
Prize Collecting Steiner tree.
References: | Chapter 4, Shmoys and Williamsons.
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- Meeting 31 : Wed, Mar 04, 12:00 pm-12:50 pm -
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Exercises | |
Reading | |
Prize Collecting Steiner tree.
- Meeting 32 : Fri, Mar 06, 11:00 am-11:50 am -
References | |
Exercises | |
Reading | |
Non-Instructional Day (Holi).
- Meeting 33 : Mon, Mar 09, 09:00 am-09:50 am - Narayanaswamy
References | |
Exercises | |
Reading | |
Discussion about generic framework of casting combinatorial problems as LPs and Vector programs. How does one round in this setting of vector programs? Choose a random hyperplane passing through the origin. How does one choose this plane?
Vertex cover LP. Recall 1/2 integrality of Vertex cover LP. Nemhauser Trotter theorem and its proof.
References: | Hochbaum's book
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- Meeting 34 : Tue, Mar 10, 08:00 am-08:50 am -
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Exercises | |
Reading | |
MAX SAT and MAX CUT: randomized rounding. A simple 1/2 approximation using randomized rounding for both problems. Derandomization.
References: | Chapter 5 (Sections 5.1, 5.2, 5.3) Shmoys and Williamsons.
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- Meeting 35 : Wed, Mar 11, 12:00 pm-12:50 pm -
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Exercises | |
Reading | |
MAX SAT continued. Randomized rounding. Choosing the better of the 2 solutions. A 3/4 approximation algorithm.
References: | Chapter 5 (Sections 5.3, 5.4) Shmoys and Williamsons.
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- Meeting 36 : Fri, Mar 13, 11:00 am-11:50 am -
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Exercises | |
Reading | |
Prize collecting Steiner tree. Randomized Rounding approach. (Recall deterministic rounding gives 3-approx). Goal to improve the approx. guarantee.
References: | Chapter 5 (Section 5.7) Shmoys and Williamsons.
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- Meeting 37 : Mon, Mar 16, 09:00 am-09:50 am -
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Exercises | |
Reading | |
Prize collecting Steiner Tree: randomized rounding analysis completed.
Vertex coloring. Promise problems -- 3 colorable graphs. A simple O(sqrt(n)) algorithm using the following 2 observations -- i) every graph is vertex colorable using Delta+1 colors. ii) If a graph is 3-colorable, then for every vertex its neighbourhood is 2-colorable.
References: | Chapter 5 (section 5.12) Shmoys and Williamsons.
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- Meeting 38 : Tue, Mar 17, 08:00 am-08:50 am - Narayanaswamy
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Exercises | |
Reading | |
Application of chernoff bounds to 3 colouring dense graphs - a random sample of vertices with a good probabiliyt is a small dominating set. Two events here - Small set and Dominating set.
In both chernoff bound used to bound deviations from expectation.
References: | Shmoys and WIlliamson, chapter 5.
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- Meeting 39 : Wed, Mar 18, 06:00 am-06:00 am - Narayanaswamy
References | |
Exercises | |
Reading | |
Summarizing the line of thought in Randomised Rounding-
a. Design probability distributions and get a handle on expectation and
derandomize using conditional probability.
b. For distributions, get a handle for expectation, and bound deviation, and get a good running time with high probability.
c. Where do distributions come from: use LP optimum points a probability distributions (carefully), like in MAXSAT, and then take better of two distributions.
d. There are better distributions- sneak preview into MAXCUT, assign vectors to vertices and design a cost function, and use a nice rounding technique. Summary, there are better distributions!! for MAXCUT. How good can these distributions become?
References: | Shmoys and WIlliamson - Chapter 6 and Chapter 5
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- Meeting 40 : Fri, Mar 20, 11:00 am-11:50 am - Meghana
References | |
Exercises | |
Reading | |
Discussion of quiz sheets
- Meeting 41 : Mon, Mar 23, 09:00 am-09:50 am - Narayanaswamy
References | |
Exercises | |
Reading | |
Application of Chernoff Bounds to Integer Multicommodity Flow.
References: | Shmoys and Williamson, Chapter 5.
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- Meeting 42 : Tue, Mar 24, 08:00 am-08:50 am - Narayanaswamy
References | |
Exercises | |
Reading | |
Introduction to the geometry of Linear programming and its application in approximation algorithms.
References: | Geometric Algorithms and Combinatorial Optimisation : preliminaries chapter, and chapter on ellipsoid method.
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- Meeting 43 : Wed, Mar 25, 06:00 am-06:00 am -
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Exercises | |
Reading | |
Discussion of the ellipsoid method and ellipsoid template. The role of the separation oracle to find violated inequalities.
References: | Groetschel Lovasz Schrijver, Chapter on the Ellipsoid method.
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- Meeting 44 : Fri, Mar 27, 11:00 am-11:50 am -
References | |
Exercises | |
Reading | |
Introduction to positive semidefinite matrices. The structure of symmetric matrices with real valued entries. Decomposing the range of the linear transformation into eigen spaces. Characterisation of positive semidefinite real symmetric matrices. The usage in vector programs
References: | Chapter 6 of SHmoys and Williamson
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- Meeting 45 : Mon, Mar 30, 09:00 am-09:50 am -
References | |
Exercises | |
Reading | |
Vector program relaxation of max-cut. Rounding using the solution to the vector program. Derandomizing using a random hyperplane containing the origin. How to sample a random hyperplane? What is the probability that the vectors given to end points of an edge fall on different sides of the hyperplane.
References: | Shmoys and williamson chapter 6
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- Meeting 46 : Tue, Mar 31, 08:00 am-08:50 am -
References | |
Exercises | |
Reading | |
Completing the vector program analysis of max-cut.
Introduction to approximate quadratic programming
References: | shmoys and williamson chapter 6
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- Meeting 47 : Wed, Apr 01, 06:00 am-06:00 am -
References | |
Exercises | |
Reading | |
Vector programs for approximate quadratic programming in which coefficients can be of arbitrary value, but the coefficient matrix is semidefinite. Using mclaurin's series to give a good approximation to arcsin(x), and application of the pointwise product operator on positive semidefinite matrices. Setting up the approximation
References: | Shmoys and williamson, 6th chapter.
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- Meeting 48 : Fri, Apr 03, 11:00 am-11:50 am -
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Exercises | |
Reading | |
holiday
- Meeting 49 : Mon, Apr 06, 09:00 am-09:50 am -
References | |
Exercises | |
Reading | |
SDP study of colouring 3 colourable graphs.
References: | Shmoys and williamson chapter 6
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- Meeting 50 : Tue, Apr 07, 08:00 am-08:50 am -
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Exercises | |
Reading | |
SDP for 3 coloring and subsequent randomised rounding
References: | shmoys and williamson chapter 6
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- Meeting 51 : Wed, Apr 08, 06:00 am-06:00 am -
References | |
Exercises | |
Reading | |
SDP for coloring 3 colorable graphs.
Introduction to role of complementary slackness, and the Primal-Dual template
References: | Chapter 7 Shmoys and Williamson
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- Meeting 52 : Fri, Apr 10, 11:00 am-11:50 am -
References | |
Exercises | |
Reading | |
Class cancelled due to Biplav visit
- Meeting 53 : Mon, Apr 13, 09:00 am-09:50 am -
References | |
Exercises | |
Reading | |
Primal dual for set cover.
References: | shmoys and williamson chapter 7
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- Meeting 54 : Tue, Apr 14, 08:00 am-08:50 am -
References | |
Exercises | |
Reading | |
Primal Dual for set cover, mention of special kinds of set cover restrictions that this could be used for.
Cycle hitting sets - feedback vertex cover introduced
References: | shmoys and williamson
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- Meeting 55 : Wed, Apr 15, 06:00 am-06:00 am -
References | |
Exercises | |
Reading | |
Feedback vertex set primal -dual, logn approximation.
careful choice of cycle whose corresponding dual variable need to be increased. Introduction to the s-t shortest path LP, and suggestion of
understanding Dijkstra as primal dual. Introduction to Generalized steiner tree
References: | shmoys and williamson
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- Meeting 56 : Fri, Apr 17, 11:00 am-11:50 am -
References | |
Exercises | |
Reading | |
class cancelled due to unforeseen circumstances
- Meeting 57 : Mon, Apr 20, 09:00 am-09:50 am -
References | |
Exercises | |
Reading | |
Primal-Dual generalized steiner tree
References: | Shmoys and wiliamsson
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- Meeting 58 : Tue, Apr 21, 08:00 am-08:50 am -
References | |
Exercises | |
Reading | |
Primal Dual Generalized Steiner tree
References: | shmoys and williamson
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- Meeting 59 : Wed, Apr 22, 06:00 am-06:00 am -
References | |
Exercises | |
Reading | |
Primal dual - Geoemetric set cover, hardness of setcover with intersections 1.
References: | shmoys and williamson
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- Meeting 60 : Fri, Apr 24, 11:00 am-11:50 am -
References | |
Exercises | |
Reading | |
Line segment cover- lp formulation
References: | Meggido and Tamir - google key word
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- Meeting 61 : Mon, Apr 27, 09:00 am-09:50 am -
References | |
Exercises | |
Reading | |
To Be Announced
- Meeting 62 : Tue, Apr 28, 08:00 am-08:50 am -
References | |
Exercises | |
Reading | |
To Be Announced
- Meeting 63 : Wed, Apr 29, 12:00pm-12:50pm -
References | |
Exercises | |
Reading | |
To Be Announced