Orca is an efficient algorithm for counting graphlets in networks. It computes node- and edge-orbits (of 4- and 5-node graphlets) for each node in the network.

Orca is implemented as a simple command-line utility that consists of a single C++ source file. It has no external dependencies and requires only a relatively modern compiler that supports unordered_map from the C++11 standard, which most do.

Current GCC compiler requires a -std=c++11 flag. For example, you can compile the source using MinGW compiler on Windows with: g++ -O2 -std=c++11 -o orca.exe orca.cpp

The utility takes four command-line arguments: orca.exe node 5 graph.in orbit-counts.out

1. Orbit type is either node or edge.
2. Graphlet size indicates the size of graphlets that you wish to count and should be either 4 or 5.
3. Input file describes the network in a simple text format. The first line contains two integers n and e - the number of nodes and edges. The following e lines describe undirected edges with space-separated ids of their endpoints. Node ids should be between 0 and n-1. See graph.in as an example.
4. Output file will consist of n lines, one for each node in a graph from 0 to n-1. Every line will contain space-separated orbit counts depending on the specified graphlet size and orbit type.

The random Erdos-Renyi graphs used in experiments are available in the random_graphs.zip archive.