Signed graph
![There are eight ways that signs can be assigned to the sides of a triangle. An odd number of negative signs makes an unbalanced triangle, Fritz Heider said.](/Images/godic/202502/11/Pox1031.jpg")
In the area of graph theory in mathematics, a signed graph is a graph in which each edge has a positive or negative sign.
Two fundamental questions about a signed graph are: Is it balanced? What is the largest size of a balanced edge set in it? The first question is not difficult; the second is computationally intractable (technically, it is NP-hard).