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Wilfried Imrich (born 25 May 1941) is an Austrian mathematician working mainly in graph theory.He is known for his work on graph products, and authored the books Product Graphs: Structure and Recognition (Wiley, 2000, with Sandi Klavžar), [1] Topics in graph theory: Graphs and their Cartesian Products (AK Peters, 2008, with Klavžar and Douglas F. Rall), [2] and Handbook of Product Graphs ...
In graph theory, a graph product is a binary operation on graphs. Specifically, it is an operation that takes two graphs G 1 and G 2 and produces a graph H with the following properties: The vertex set of H is the Cartesian product V ( G 1 ) × V ( G 2 ) , where V ( G 1 ) and V ( G 2 ) are the vertex sets of G 1 and G 2 , respectively.
If a connected graph is a Cartesian product, it can be factorized uniquely as a product of prime factors, graphs that cannot themselves be decomposed as products of graphs. [2] However, Imrich & Klavžar (2000) describe a disconnected graph that can be expressed in two different ways as a Cartesian product of prime graphs:
Another model, which generalizes Gilbert's random graph model, is the random dot-product model. A random dot-product graph associates with each vertex a real vector. The probability of an edge uv between any vertices u and v is some function of the dot product u • v of their respective vectors.
Powers of graphs are referred to using terminology similar to that of exponentiation of numbers: G 2 is called the square of G, G 3 is called the cube of G, etc. [1] Graph powers should be distinguished from the products of a graph with itself, which (unlike powers) generally have many more vertices than the original graph.
Klavžar's research concerns graph products, metric graph theory, chemical graph theory, graph domination, and the Tower of Hanoi. Together with Wilfried Imrich and Richard Hammack, he is the author of the book Handbook of Product Graphs (CRC Press, 2011).
The strong product is one of several different graph product operations that have been studied in graph theory. The strong product of any two graphs can be constructed as the union of two other products of the same two graphs, the Cartesian product of graphs and the tensor product of graphs. An example of a strong product is the king's graph ...
If H is a two-vertex complete graph K 2, then for any graph G, the rooted product of G and H has domination number exactly half of its number of vertices. Every connected graph in which the domination number is half the number of vertices arises in this way, with the exception of the four-vertex cycle graph.