If a simple graph has diameter greater than 3, then its complement has diameter less than 3:
The graph diameter is unchanged when reversing every edge:
The graph radius does change:
Illustrate the diameter in two Petersen graphs:
For a
WheelGraph of size 5 or more, the diameter is 2:
A
WheelGraph of size 4 is a complete graph, so the diameter is 1: