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The goal is to find a fractional set cover in which the sum of fractions is as small as possible. Note that a (usual) set cover is equivalent to a fractional set cover in which all fractions are either 0 or 1; therefore, the size of the smallest fractional cover is at most the size of the smallest cover, but may be smaller.
Geometric combinatorics is a branch of mathematics in general and combinatorics in particular. It includes a number of subareas such as polyhedral combinatorics (the study of faces of convex polyhedra), convex geometry (the study of convex sets, in particular combinatorics of their intersections), and discrete geometry, which in turn has many applications to computational geometry.
Combinatorics is an area of mathematics primarily concerned with counting, both as a means and as an end to obtaining results, and certain properties of finite structures.It is closely related to many other areas of mathematics and has many applications ranging from logic to statistical physics and from evolutionary biology to computer science.
In combinatorics, stars and bars (also called "sticks and stones", [1] "balls and bars", [2] and "dots and dividers" [3]) is a graphical aid for deriving certain combinatorial theorems. It can be used to solve a variety of counting problems , such as how many ways there are to put n indistinguishable balls into k distinguishable bins. [ 4 ]
The bipartite double cover of the Petersen graph is the Desargues graph: K 2 × G(5,2) = G(10,3). The bipartite double cover of a complete graph K n is a crown graph (a complete bipartite graph K n,n minus a perfect matching). In particular, the bipartite double cover of the graph of a tetrahedron, K 4, is the graph of a cube.
The Fano matroid, derived from the Fano plane.Matroids are one of many kinds of objects studied in algebraic combinatorics. Algebraic combinatorics is an area of mathematics that employs methods of abstract algebra, notably group theory and representation theory, in various combinatorial contexts and, conversely, applies combinatorial techniques to problems in algebra.
A good cover is an open cover in which all sets and all non-empty intersections of finitely-many sets are contractible (Petersen 2006). The concept was introduced by André Weil in 1952 for differentiable manifolds , demanding the U α 1 … α n {\displaystyle U_{\alpha _{1}\ldots \alpha _{n}}} to be differentiably contractible.
Extremal combinatorics is a field of combinatorics, which is itself a part of mathematics.Extremal combinatorics studies how large or how small a collection of finite objects (numbers, graphs, vectors, sets, etc.) can be, if it has to satisfy certain restrictions.