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Free Matroid
In mathematics, the free matroid over a given ground-set ''E'' is the matroid in which the independent sets are all subsets of ''E''. It is a special case of a uniform matroid. The unique basis Basis may refer to: Finance and accounting * Adjusted basis, the net cost of an asset after adjusting for various tax-related items *Basis point, 0.01%, often used in the context of interest rates * Basis trading, a trading strategy consisting ... of this matroid is the ground-set itself, ''E''. Among matroids on ''E'', the free matroid on ''E'' has the most independent sets, the highest rank, and the fewest circuits. Free extension of a matroid The free extension of a matroid M by some element e\not\in M, denoted M+e, is a matroid whose elements are the elements of M plus the new element e, and: * Its circuits are the circuits of M plus the sets B\cup \ for all bases B of M. * Equivalently, its independent sets are the independent sets of M plus the sets I\cup \ for all independ ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Matroid
In combinatorics, a branch of mathematics, a matroid is a structure that abstracts and generalizes the notion of linear independence in vector spaces. There are many equivalent ways to define a matroid axiomatically, the most significant being in terms of: independent sets; bases or circuits; rank functions; closure operators; and closed sets or flats. In the language of partially ordered sets, a finite matroid is equivalent to a geometric lattice. Matroid theory borrows extensively from the terminology of both linear algebra and graph theory, largely because it is the abstraction of various notions of central importance in these fields. Matroids have found applications in geometry, topology, combinatorial optimization, network theory and coding theory. Definition There are many equivalent ( cryptomorphic) ways to define a (finite) matroid.A standard source for basic definitions and results about matroids is Oxley (1992). An older standard source is Welsh (1976). See Brylawsk ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Uniform Matroid
In mathematics, a uniform matroid is a matroid in which the independent sets are exactly the sets containing at most ''r'' elements, for some fixed integer ''r''. An alternative definition is that every permutation of the elements is a symmetry. Definition The uniform matroid U^r_n is defined over a set of n elements. A subset of the elements is independent if and only if it contains at most r elements. A subset is a basis if it has exactly r elements, and it is a circuit if it has exactly r+1 elements. The rank of a subset S is \min(, S, ,r) and the rank of the matroid is r. A matroid of rank r is uniform if and only if all of its circuits have exactly r+1 elements. The matroid U^2_n is called the n-point line. Duality and minors The dual matroid of the uniform matroid U^r_n is another uniform matroid U^_n. A uniform matroid is self-dual if and only if r=n/2. Every minor of a uniform matroid is uniform. Restricting a uniform matroid U^r_n by one element (as long as r 0) prod ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Basis Of A Matroid
In mathematics, a basis of a matroid is a maximal independent set of the matroid—that is, an independent set that is not contained in any other independent set. Examples As an example, consider the matroid over the ground-set R2 (the vectors in the two-dimensional Euclidean plane), with the following independent sets: It has two bases, which are the sets , . These are the only independent sets that are maximal under inclusion. The basis has a specialized name in several specialized kinds of matroids: * In a graphic matroid, where the independent sets are the forests, the bases are called the ''spanning forests'' of the graph. * In a transversal matroid, where the independent sets are endpoints of matchings in a given bipartite graph, the bases are called ''transversals''. * In a linear matroid, where the independent sets are the linearly-independent sets of vectors in a given vector-space, the bases are just called ''bases'' of the vector space. Hence, the concept of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Circuit Of A Matroid
In mathematics, a basis of a matroid is a maximal independent set of the matroid—that is, an independent set that is not contained in any other independent set. Examples As an example, consider the matroid over the ground-set R2 (the vectors in the two-dimensional Euclidean plane), with the following independent sets: It has two bases, which are the sets , . These are the only independent sets that are maximal under inclusion. The basis has a specialized name in several specialized kinds of matroids: * In a graphic matroid, where the independent sets are the forests, the bases are called the ''spanning forests'' of the graph. * In a transversal matroid, where the independent sets are endpoints of matchings in a given bipartite graph, the bases are called ''transversals''. * In a linear matroid, where the independent sets are the linearly-independent sets of vectors in a given vector-space, the bases are just called ''bases'' of the vector space. Hence, the concept of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
