Option A : TrueLet’s think about what (A
2)
i,i , the i - th term on the diagonal is. We have
But Aij =Aj , i, assuming that the graph is undirected, and A
ji = 1(i ~ j), i.e. is 1 is i and j are adjacent and 0 otherwise. Thus A
ijA
j,i = A
2i,j = A
i,j = 1(i ~ j) So the sum is just the number of j such that i ~ j, which
precisely the degree is.
This work if vertices in your graph may have a single self-loop, provided you count that as 1 (not 2) for the degree. Indeed, the term in the sum when j = i is just A
2i,i, but you need this to be equal to A
i,i.
Thus it needs to be 0 or 1.
It does not work more generally, however, as A
2ii ≠ A
i,j if A
i,j > 1.
even for an undirected graph, provided the graph is simple.
Option : B False.A cyclic graph is a graph containing at least one graph cycle. Consider a graph with 10 vertices where only three vertices form a cycle while reset are isolated vertices (that is a disconnected graph)
In such a case, sum of all the elements of A is (1 + 1 + 1) = 3 and 3 is less than 2 (10 -1) = 2 * 9 = 18. But the graph is still cyclic.
Option C : True.The matrix A
n-1 + In represents number paths upto length n - 1 between pair of vertices, for a connected graph there will be at least one path between each pair of vertices, thus all entries of A
n-1 + I
n will be non zero.
Option D : FalseConsidering the following adjacency matrix :
The corresponding graph is :
The graph is not connected