Quick Start

This guide demonstrates the essential features of graphstruc to get you started quickly.

Basic Usage

Creating a simple undirected graph with vertices and edges:

use graphstruc, only: graph_type
type(graph_type) :: graph

! Add vertices with 2D feature vectors
call graph%add_vertex(feature=[1.0, 2.0])
call graph%add_vertex(feature=[3.0, 4.0])

! Connect vertices with a weighted edge
call graph%add_edge(index=[1, 2], weight=1.5)

! Query graph properties
write(*,*) graph%num_vertices, graph%num_edges

! Clean up when finished
call graph%clear()

The first vertex you add determines the feature vector size for all subsequent vertices.

Directed Graphs

For directed graphs, set the directed property and use negative indices for the target vertex:

graph%directed = .true.

! Create directed edge from vertex 1 to vertex 2
call graph%add_edge(index=[1, -2])  ! 1 → 2

! Alternatively, use the directed parameter
call graph%add_edge(index=[1, 2], directed=.true.)

This convention allows you to have both directed and undirected edges in the same graph.

Sparse Storage

For large or sparse graphs, convert to Compressed Sparse Row (CSR) format for better memory efficiency:

! Build graph in default dense format
do i = 1, 1000
  call graph%add_vertex()
end do

! Add edges
do i = 1, 5000
  call graph%add_edge(index=[src(i), tgt(i)])
end do

! Convert to sparse format (O(V+E) memory instead of O(V²))
call graph%convert_to_sparse()

Sparse format is particularly beneficial when the number of edges is much smaller than V².

Common Operations

Removing vertices and edges:

! Remove multiple vertices (and their connected edges)
call graph%remove_vertices([2, 4])

! Remove specific edges
call graph%remove_edges([1, 3])

Working with self-loops:

! Add self-loops to all vertices
call graph%add_self_loops()

! Add to specific vertices with custom weight
call graph%add_self_loops(indices=[1, 3, 5], weight=2.0)

Calculating vertex degrees:

! Calculate degree for all vertices
call graph%calculate_degree()

! Access individual vertex degrees
write(*,*) 'Vertex 1 degree:', graph%vertex(1)%degree

Copying graphs:

! Create a duplicate graph
call graph2%copy(graph1)

! Copy and convert format simultaneously
call graph2%copy(graph1, sparse=.true.)

Next Steps

For more detailed information: