Horst Sachs (27 March 1927 – 25 April 2016) was a German

mathematician A mathematician is someone who uses an extensive knowledge of mathematics in their work, typically to solve mathematical problems. Mathematicians are concerned with numbers, data, quantity, mathematical structure, structure, space, Mathematica ...

, an expert in

graph theory In mathematics and computer science, graph theory is the study of ''graph (discrete mathematics), graphs'', which are mathematical structures used to model pairwise relations between objects. A graph in this context is made up of ''Vertex (graph ...

, a recipient of the Euler Medal (2000). He earned the degree of

Doctor of Science A Doctor of Science (; most commonly abbreviated DSc or ScD) is a science doctorate awarded in a number of countries throughout the world. Africa Algeria and Morocco In Algeria, Morocco, Libya and Tunisia, all universities accredited by the s ...

(Dr. rer. nat.) from the Martin-Luther-Universität Halle-Wittenberg in 1958. Following his retirement in 1992, he was

professor emeritus ''Emeritus/Emerita'' () is an honorary title granted to someone who retirement, retires from a position of distinction, most commonly an academic faculty position, but is allowed to continue using the previous title, as in "professor emeritus". ...

at the Institute of Mathematics of the

Technische Universität Ilmenau The Technische Universität Ilmenau (''Ilmenau University of Technology'', TU Ilmenau) is a German public research university located in Ilmenau, Thuringia, central Germany. Founded in 1894, it has five academic departments (faculties) with ...

. His encyclopedic book in

spectral graph theory In mathematics, spectral graph theory is the study of the properties of a Graph (discrete mathematics), graph in relationship to the characteristic polynomial, eigenvalues, and eigenvectors of matrices associated with the graph, such as its adjacen ...

, ''Spectra of Graphs. Theory and Applications'' (with Dragos Cvetković and Michael Doob) has several editions and was translated in several languages.Review by P. Rowlinson (1996), ''Proceedings of the Edinburgh Mathematical Society (Series 2)'' 39: 188–189, . Two theorems in graph theory bear his name. One of them relates the coefficients of the

characteristic polynomial In linear algebra, the characteristic polynomial of a square matrix is a polynomial which is invariant under matrix similarity and has the eigenvalues as roots. It has the determinant and the trace of the matrix among its coefficients. The ...

of a graph to certain structural features of the graph. Another one is a simple relation between the characteristic polynomials of a graph and its

line graph In the mathematics, mathematical discipline of graph theory, the line graph of an undirected graph is another graph that represents the adjacencies between edge (graph theory), edges of . is constructed in the following way: for each edge i ...

. Sachs subgraphs are also named after Sachs.

References

1927 births 20th-century German mathematicians Graph theorists 2016 deaths Academic staff of Technische Universität Ilmenau {{Germany-mathematician-stub