Coloring Problems
DIMACS Graph Format

Last revision: May 08, 1993
Abbreviated: Bart Massey March 02, 2001


One purpose of the DIMACS Challenge is to ease the effort required to test and compare algorithms and heuristics by providing a common testbed of instances and analysis tools. To facilitate this effort, a standard format must be chosen for the problems addressed. This document outlines a format for graphs that is suitable for those looking at graph coloring. This format extends to a flexible format suitable for many types of graph and network problems. This format was also the format chosen for the First Computational Challenge on network flows and matchings.

Input Files

An input file contains all the information about a graph needed to define a coloring problem.

In this format, nodes are numbered from 1 up to n edges in the graph.

Files are assumed to be well-formed and internally consistent: node identifier values are valid, nodes are defined uniquely, exactly m edges are defined, and so forth.

Output Files

Every algorithm or heuristic should create an output file. This output file should consist of one or more of the following lines, depending on the type of algorithm and problem being solved.

Exemples :

c FILE: myciel3.col
c SOURCE: Michael Trick (
c DESCRIPTION: Graph based on Mycielski transformation.
c Triangle free (clique number 2) but increasing
c coloring number
p edge 11 20
e 1 2
e 1 4
e 1 7
e 1 9
e 2 3
e 2 6
e 2 8
e 3 5
e 3 7
e 3 10
e 4 5
e 4 6
e 4 10
e 5 8
e 5 9
e 6 11
e 7 11
e 8 11
e 9 11
e 10 11

DIMACS Project: Rutgers University
Bart Massey