The circuit rank ,
is the smallest number of graph edges which must be
removed from an undirected graph on
graph edges and
nodes such that no graph cycle
remains. The circuit rank also gives the number of fundamental
cycles in a cycle basis of a graph (Harary 1994, pp. 37-40; White 2001,
p. 56). The concept was first introduced by Gustav Kirchhoff (Kirchhoff 1847;
Veblen 1916, p. 9; Kotiuga 2010, p. 20), and has been referred to by a
number of different names and symbols as summarized in the following tables.
| name | references |
| circuit rank | |
| cycle rank | Harary (1994, p. 39), White (2001, p. 56), Gross and Yellen (2006, pp. 192 and 661) |
| (first) graph Betti number | White (2001), Gross and Yellen (2006, pp. 192) |
| cyclomatic number | Listing (1862), Veblen (1916, pp. 9 and 18) |
| graph nullity |
| notation | references |
| Veblen (1916, pp. 9 and 18), Volkmann (1996), Babić et al. (2002) | |
| Gross and Yellen (2006, pp. 192 and 661), White (2001, p. 56) | |
| Harary (1994, p. 39) |
For a graph with edge count , vertex count
, and
connected components,
the circuit rank is given by
|
(1)
|
The notation
for circuit rank is unrelated to the
used for the mutual-visibility
number, the
of the matching polynomial, and the
parameter of a strongly
regular graph.
The circuit rank provides an inequality on the total number of undirected graph cycles
given by
|
(2)
|
(Kirchhoff 1847, Ahrens 1897, König 1936, Volkmann 1996). Furthermore,
|
(3)
|
iff any two cycles have no edge in common (Volkmann 1996). Among connected graphs, the equality therefore holds for (and only for) cactus
graphs. Mateti and Deo (1976) proved that there are "essentially" only
four graphs with :
the complete graphs
and
, the complete bipartite
graph
,
and
(Volkmann 1996).
Precomputed values for many graphs is implemented in the Wolfram Language as GraphData[g, "CircuitRank"].