Read

read(graph_file: str) → ProblemData[source]

Read graph file and return a ProblemData object.

Automatically detects graph file format (adjacency list or edge list) and reads data accordingly.

Parameters:

graph_file (str) – Path to graph file (adjacency list or edge list format).

Returns:

A ProblemData object containing the graph data.

Return type:

ProblemData

Raises:
read_adjacency_list_format(filename: str) → ProblemData[source]

Read data from adjacency list format file.

Adjacency list format: each line represents a node and its neighbors, formatted as “node_id neighbor1 neighbor2 …”

Parameters:

filename (str) – Path to file.

Returns:

Initialized ProblemData object.

Return type:

ProblemData

Raises:

RuntimeError – When file cannot be opened or has invalid format.

read_edge_list_format(filename: str) → ProblemData[source]

Read data from edge list format file.

Edge list format: typically contains a header line “p edge num_nodes num_edges”, followed by lines representing edges formatted as “e node1 node2”

Parameters:

filename (str) – Path to file.

Returns:

Initialized ProblemData object.

Return type:

ProblemData

Raises:

RuntimeError – When file cannot be opened or has invalid format.

File Formats

Adjacency List Format

In adjacency list format, the first line contains the number of nodes. Each subsequent line represents a node and its neighbors in the format: node_id: neighbor1 neighbor2 ...

Example file: ``graph.txt``

4
0: 1 2 3
1: 0 2
2: 0 1 3
3: 0 2

This represents a graph with 4 nodes where:

  • Node 0 is connected to nodes 1, 2, 3

  • Node 1 is connected to nodes 0, 2

  • Node 2 is connected to nodes 0, 1, 3

  • Node 3 is connected to nodes 0, 2

Usage example:

import pycnp

problem = pycnp.read_adjacency_list_format("graph.txt")

Note

This format is used by instances such as ErdosRenyi_n235.txt.

Edge List Format

In edge list format, the first line is a header p edge num_nodes num_edges, followed by edge definitions e node1 node2.

Example file: ``graph.txt``

p edge 4 5
e 0 1
e 0 2
e 0 3
e 1 2
e 2 3

This represents a graph with 4 nodes and 5 edges:

  • Edge between node 0 and node 1

  • Edge between node 0 and node 2

  • Edge between node 0 and node 3

  • Edge between node 1 and node 2

  • Edge between node 2 and node 3

Usage example:

import pycnp

problem = pycnp.read_edge_list_format("graph.txt")

Note

This format is used by instances such as hi_tech.txt. The read() function automatically detects the format based on the presence of the p header line, so you typically only need to use it.