The concepts of L-convex function and M-convex function have recently been introduced by Murota as generalizations of submodular function and base polyhedron, respectively, and discrete separation theorems are established for L-convex/concave functions and for M-convex/concave functions as generalizations of Frank's discrete separation theorem for submodular/supermodular set functions and Edmon...

Let k be an integer exceeding one. The class of k–regular matroids is a generalization of the classes of regular and near-regular matroids. A simple rank–r regular matroid has the maximum number of points if and only if it is isomorphic to M(Kr+1), the cycle matroid of the complete graph on r + 1 vertices. A simple rank–r near-regular matroid has the maximum number of points if and only if it i...

Random sampling is a powerful tool for gathering information about a group by considering only a small part of it. We discuss some broadly applicable paradigms for using random sampling in combinatorial optimization, and demonstrate the eeectiveness of these paradigms for two optimization problems on matroids: nding an optimum matroid basis and packing disjoint matroid bases. Applications of th...

Following a conjecture of Sugihara, we characterize, combinatorially, the plane pictures of vertices and faces which lift to sharp three-dimensional scenes with plane faces. We also prove two generalizations of Laman's theorem on infinitesimally rigid plane frameworks. Both results are special cases of a representation theorem for the k-plane matroid of an incidence graph G = (A, B; I). The ind...

We study new posetsQ obtained by removing from a geometric latticeL of a biased graph certain flats indexed by a simplicial complex C. (One example of L is the lattice of flats of the vector matroid of a root system Bn.) We study the structure and compute the characteristic polynomial ofQ. With certain choices of L and C, including ones for which Q is a lattice interpolating between those of Bn...

The closed fuzzy matroid is a subsystem of the fuzzy matroid theory. Some important conclusions, ideas and methods of the closed fuzzy matroid are briefly introduced and commented in this paper. We try to let readers to know the latest development and results of the closed fuzzy matroids.

Let F4 be the root system associated with the 24-cell, and let M(F4) be the simple linear dependence matroid corresponding to this root system. We determine the automorphism group of this matroid and compare it to the Coxeter group W for the root system. We find non-geometric automorphisms that preserve the matroid but not the root system.

We show that the set of r-quasi-transversals of a matroid, if nonempty, is the set of bases of a matroid. We also give an alternative proof of the known theorem which identifies the conjugate of the rank partition of a matroid.