Connected graphs

Question 1

When is an undirected graph weakly connected?

Answer 1

There exists an edge between each pair of vertices u v

Question 2

When is a digraph weakly connected?

Answer 2

If a u-> v semi-path exists for every pair of vertices u v

Question 3

When is a graph strongly connected?

Answer 3

Both a u -> v and a v -> u path exist in igraph for each pair of vertices u and v