Diameter is defined as the longest of all shortest paths in a graph.
graph_diameter( apsp_table, output_table )
Arguments
TEXT. Name of the output table generated by a prior run of all pairs shortest path (APSP).
TEXT. Name of the table to store the diameter. It contains a row for every group, the diameter value and the two vertices that are the farthest apart.
DROP TABLE IF EXISTS vertex, edge; CREATE TABLE vertex( id INTEGER, name TEXT ); CREATE TABLE edge( src_id INTEGER, dest_id INTEGER, edge_weight FLOAT8 ); INSERT INTO vertex VALUES (0, 'A'), (1, 'B'), (2, 'C'), (3, 'D'), (4, 'E'), (5, 'F'), (6, 'G'), (7, 'H'); INSERT INTO edge VALUES (0, 1, 1.0), (0, 2, 1.0), (0, 4, 10.0), (1, 2, 2.0), (1, 3, 10.0), (2, 3, 1.0), (2, 5, 1.0), (2, 6, 3.0), (3, 0, 1.0), (4, 0, -2.0), (5, 6, 1.0), (6, 7, 1.0);
DROP TABLE IF EXISTS out_apsp, out_apsp_summary; SELECT madlib.graph_apsp('vertex', -- Vertex table 'id', -- Vertix id column (NULL means use default naming) 'edge', -- Edge table 'src=src_id, dest=dest_id, weight=edge_weight', -- Edge arguments (NULL means use default naming) 'out_apsp'); -- Output table of shortest paths
DROP TABLE IF EXISTS out_diameter; SELECT madlib.graph_diameter('out_apsp', 'out_diameter'); SELECT * FROM out_diameter;
diameter | diameter_end_vertices ---------+----------------------- 14 | {{1,4}} (1 row)
DROP TABLE IF EXISTS edge_gr; CREATE TABLE edge_gr AS ( SELECT *, 0 AS grp FROM edge UNION SELECT *, 1 AS grp FROM edge WHERE src_id < 6 AND dest_id < 6 ); INSERT INTO edge_gr VALUES (4,5,-20,1);
DROP TABLE IF EXISTS out_gr, out_gr_summary; SELECT madlib.graph_apsp( 'vertex', -- Vertex table NULL, -- Vertex id column (NULL means use default naming) 'edge_gr', -- Edge table 'src=src_id, dest=dest_id, weight=edge_weight', 'out_gr', -- Output table of shortest paths 'grp' -- Grouping columns );
DROP TABLE IF EXISTS out_gr_path; SELECT madlib.graph_diameter('out_gr', 'out_gr_diameter'); SELECT * FROM out_gr_diameter ORDER BY grp;
grp | diameter | diameter_end_vertices ---—+---------—+----------------------— 0 | 14 | {{1,4}} 1 | 14 | {{1,4}} (2 rows)