We introduce bundle-free triangulations, that are free of large collection of triangles overlapping a circle empty of vertices. We prove that bundle-free Steiner triangulations can be used as an approximate solution for the minimum weight Steiner triangulation problem. We present new algorithms, implementations and experimental study for computing minimum weight Steiner triangulations.

The q-analogs of basic designs are discussed. It is proved that the existence of any unknown Steiner structures, the q-analogs of Steiner systems, implies the existence of unknown Steiner systems. Optimal q-analogs covering designs are presented. Some lower and upper bounds on the sizes of q-analogs covering designs are proved.

We consider the problem of finding a shortest rectilinear Steiner tree for a given set of points in the plane in the presence of rectilinear obstacles that must be avoided. We extend the Steiner ratio to the obstacle-avoiding case and show that it is equal to the Steiner ratio for the obstacle-free case.

Block-intersection graphs of Steiner triple systems are considered. We prove that the block-intersection graphs of non-isomorphic Steiner triple systems are themselves non-isomorphic. We also prove that each Steiner triple system of order at most 15 has a Hamilton decomposable block-intersection graph.

lichenized mycota of the southern part of Iran including Kerman province has been poorly studied compared to the Northern Iranian provinces such as Azerbaijan, Golestan or Mazandaran. Here we present the first lichen checklist for Kerman province, which comprises 57 species in 30 genera and 14 families. For this purpose, we reviewed both old and recent literature, examined herbarium collections...

Let G be a connected graph and S a nonempty set of vertices of G. Then the Steiner distance d,(S) of S is the smallest number of edges in a connected subgraph of G that contains S. Let k, I, s and m be nonnegative integers with m > s > 2 and k and I not both 0. Then a connected graph G is said to be k-vertex I-edge (s,m)-Steiner distance stable, if for every set S of s vertices of G with d,(S) ...

The Steiner tree problem asks for a minimum cost tree spanning a given set of terminals S ⊆ V in a weighted graph G = (V, E, c), c : E → R. In this paper we consider a generalization of the Steiner tree problem, so called Polymatroid Steiner Problem, in which a polymatroid P = P (V ) is defined on V and the Steiner tree is required to span at least one base of P (in particular, there may be a s...

We consider the vertex-weighted version of the undirected Steiner tree problem. In this problem, a cost is incurred both for the vertices and the edges present in the Steiner tree. We completely describe the associated polytope by linear inequalities when the underlying graph is series-parallel. For general graphs, this formulation can be interpreted as a (partial) extended formulation for the ...

The line planning problem in public transport deals with the construction of a system of lines that is both attractive for the passengers and of low costs for the operator. In general, the computed line system should be connected, i.e., for each two stations there have to be a path that is covered by the lines. This subproblem is a generalization of the well-known Steiner tree problem; we call ...