Suppose $G$ is a controllable graph of order $n$ with adjacency matrix $A$. Let $W=[e,Ae,\ldots,A^{ n-1}e]$ ($e$ is the all-one vector) and $\Delta=\prod_{ i>j}(\alpha_i-\alpha_j)^2$ ($\alpha_i$'s are eigenvalues of $A$) be the walk matrix and the discriminant of $G$, respectively. Wang and Yu \cite{ wangyu2016} showed that if $$\theta(G):=\gcd\{ 2^{ -\lfloor\frac{ n}{ 2}\rfloor}\det W,\Delta\} $$ is odd and squarefree, then $G$ is determined by its generalized spectrum (DGS). Using the primary decomposition theorem, we obtain a new criterion for a graph $G$ to be DGS without the squarefreeness assumption on $\theta(G)$. Examples are further given to illustrate the effectiveness of the proposed criterion, compared with the two existing methods to deal with the difficulty of non-squarefreeness.
Categories: math.CO