Parameterized complexity | Computational complexity theory

Parameterized complexity

In computer science, parameterized complexity is a branch of computational complexity theory that focuses on classifying computational problems according to their inherent difficulty with respect to multiple parameters of the input or output. The complexity of a problem is then measured as a function of those parameters. This allows the classification of NP-hard problems on a finer scale than in the classical setting, where the complexity of a problem is only measured as a function of the number of bits in the input. The first systematic work on parameterized complexity was done by . Under the assumption that P ≠ NP, there exist many natural problems that require superpolynomial running time when complexity is measured in terms of the input size only, but that are computable in a time that is polynomial in the input size and exponential or worse in a parameter k. Hence, if k is fixed at a small value and the growth of the function over k is relatively small then such problems can still be considered "tractable" despite their traditional classification as "intractable". The existence of efficient, exact, and deterministic solving algorithms for NP-complete, or otherwise NP-hard, problems is considered unlikely, if input parameters are not fixed; all known solving algorithms for these problems require time that is exponential (or at least superpolynomial) in the total size of the input. However, some problems can be solved by algorithms that are exponential only in the size of a fixed parameter while polynomial in the size of the input. Such an algorithm is called a fixed-parameter tractable (fpt-)algorithm, because the problem can be solved efficiently for small values of the fixed parameter. Problems in which some parameter k is fixed are called parameterized problems. A parameterized problem that allows for such an fpt-algorithm is said to be a fixed-parameter tractable problem and belongs to the class FPT, and the early name of the theory of parameterized complexity was fixed-parameter tractability. Many problems have the following form: given an object x and a nonnegative integer k, does x have some property that depends on k? For instance, for the vertex cover problem, the parameter can be the number of vertices in the cover. In many applications, for example when modelling error correction, one can assume the parameter to be "small" compared to the total input size. Then it is challenging to find an algorithm which is exponential only in k, and not in the input size. In this way, parameterized complexity can be seen as two-dimensional complexity theory. This concept is formalized as follows: A parameterized problem is a language , where is a finite alphabet. The second component is called the parameter of the problem.A parameterized problem L is fixed-parameter tractable if the question "?" can be decided in running time , where f is an arbitrary function depending only on k. The corresponding complexity class is called FPT. For example, there is an algorithm which solves the vertex cover problem in time, where n is the number of vertices and k is the size of the vertex cover. This means that vertex cover is fixed-parameter tractable with the size of the solution as the parameter. (Wikipedia).

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Karthik C. S.: Recent Hardness of Approximation results in Parameterized Complexity

In this talk, we survey some recent hardness of approximation results in parameterized complexity such as the inapproximability of the k-clique problem, provide some technical insights, and also highlight some open problems.

From playlist Workshop: Parametrized complexity and discrete optimization

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Clément Maria (10/23/19): Parameterized complexity of quantum invariants of knots

Title: Parameterized complexity of quantum invariants of knots Abstract: We give a general fixed parameter tractable algorithm to compute quantum invariants of knots presented by diagrams, whose complexity is singly exponential in the carving-width (or the tree-width) of the knot diagram.

From playlist AATRN 2019

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Shmuel Onn: Sparse integer programming is FPT

We show that sparse integer programming, in variable dimension, with linear or separable convex objective, is fixed-parameter tractable. This is a culmination of a long line of research with many colleagues. We also discuss some of the many consequences of this result, which provides a new

From playlist Workshop: Tropical geometry and the geometry of linear programming

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The chaotic complexity of natural numbers | Data structures in Mathematics Math Foundations 175

This is a sobering and perhaps disorienting introduction to the fact that arithmetic with bigger numbers starts to look quite different from the familiar arithmetic that we do with the small numbers we are used to. The notion of complexity is key in our treatment of this. We talk about bot

From playlist Math Foundations

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Hans Bodlaender: Parameterized Problems Complete for Nondeterministic FPT time and Logarithmic Space

Let XNLP be the class of parameterized problems such that an instance of size n with parameter k can be solved nondeterministically in time f(k)n to the power of O(1) and space f(k) log(n) (for some computable function f). We give a wide variety of XNLP-complete problems, such as List Colo

From playlist Workshop: Parametrized complexity and discrete optimization

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Concentration of tempered posteriors and of their variational approximations – Pierre Alquier

Many problems in science and engineering involve an underlying unknown complex process that depends on a large number of parameters. The goal in many applications is to reconstruct, or learn, the unknown process given some direct or indirect observations. Mathematically, such a problem can

From playlist Approximating high dimensional functions

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Complex Analysis Episode 14: Parameterizations

Some of the links below are affiliate links. As an Amazon Associate I earn from qualifying purchases. If you purchase through these links, it won't cost you any additional cash, but it will help to support my channel. Thank you! Complex Analysis Textbook https://amzn.to/2u5fgl4 (affiliate

From playlist Complex Analysis

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Wojciech Chachólski (4/29/20): TDA invariants and model categories

Title: TDA invariants and model categories Abstract: Data analysis is a balancing act of simplification and ignoring most of the information available on the one hand, and retaining what might be meaningful for the particular task on the other. The same balancing act of extracting simplif

From playlist AATRN 2020

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Multilevel weighted least squares polynomial approximation – Sören Wolfers, KAUST

Many problems in science and engineering involve an underlying unknown complex process that depends on a large number of parameters. The goal in many applications is to reconstruct, or learn, the unknown process given some direct or indirect observations. Mathematically, such a problem can

From playlist Approximating high dimensional functions

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Michael Farber (2/24/22): Topological complexity of spherical bundles

I will start by describing the concept of a parametrized motion planning algorithm which allows to achieve high degree of flexibility and universality. The main part of the talk will focus on the problem of understanding the parametrized topological complexity of sphere bundles. I will exp

From playlist Topological Complexity Seminar

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Daniel Kral: Parametrized approach to block structured integer programs

Integer programming is one of the most fundamental problems in discrete optimization. While integer programming is computationally hard in general, there exist efficient algorithms for special instances. In particular, integer programming is fixed parameter tractable when parameterized by

From playlist Workshop: Parametrized complexity and discrete optimization

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Complex Numbers and Addition Formulas | Algebraic Calculus One | Wild Egg

Circle geometry and related formulas in calculus are closely connected to the algebra of complex numbers. In particular the all-important rational parametrization of the unit circle has a beautiful interpretation in terms of a quadrance normalization of a square, which gives the natural as

From playlist Old Algebraic Calculus Videos

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Barbara Giunti (5/6/2020): Invariants for tame parametrised chain complexes

Title: Invariants for tame parametrised chain complexes Abstract: Along the lines traced by Wojciech Chachólski in the previous talk, we will see that model structures for persistent chain complexes lead to constructions of new and old invariants. In my talk, I will illustrate the usefuln

From playlist AATRN 2020

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Michael Farber (7/28/22): Algorithms for automated decision making and topology

Abstract: I will describe topological problems relevant to the task of creating algorithms for automated decision making. My main focus will be on motion planning algorithms in robotics although our mathematical tools are applicable to many other situations.

From playlist Applied Geometry for Data Sciences 2022

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Michal􏰀 Pilipczuk: Introduction to parameterized algorithms, lecture I

The mini-course will provide a gentle introduction to the area of parameterized complexity, with a particular focus on methods connected to (integer) linear programming. We will start with basic techniques for the design of parameterized algorithms, such as branching, color coding, kerneli

From playlist Summer School on modern directions in discrete optimization

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Parametrizing Curves in the Complex Plane 1

Complex Analysis: We give a recipe for parametrizing curves in the complex plane. Line segments are the focus of Part 1.

From playlist Complex Analysis

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Saket Saurabh: Parametrized Algorithms and possible future directions

In this talk, we will give a short overview of current research directions pursued in Parameterized Complexity and then outline a few potential research directions for further investigations.

From playlist Workshop: Parametrized complexity and discrete optimization

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Parametrizing Curves in the Complex Plane 2

Complex Analysis: We give a recipe for parametrizing curves in the complex plane. In this part, we parametrize circles and semicircles.

From playlist Complex Analysis

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Hamming weight | Clique (graph theory) | Independent set (graph theory) | Kernelization | Nondeterministic algorithm | P versus NP problem | Function (mathematics) | Computational complexity theory | Exponential time | Satisfiability | Turing machine equivalents | Reduction (complexity) | Vertex cover | Dominating set | Graph coloring