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The eigenvalues of the Hessian matrices of the generating functions for trees with $k$ components

Let us consider a truncated matroid $M_Γ^{r}$ of rank $r$ of a graphic matroid of a graph $Γ$. The basis for $M_Γ^{r}$ is the set of the forests with $r$ edges in $Γ$. We consider this basis generating function and compute its Hessian. In this paper, we show that the Hessian of the basis generating function of the truncated matroid of the graphic matroid of the complete or complete bipartite graph does not vanish by calculating the eigenvalues of the Hessian matrix. Moreover, we show that the Hessian matrix of the basis generating function of the truncated matroid of the graphic matroid of the complete or complete bipartite graph has exactly one positive eigenvalue. As an application, we show the strong Lefschetz property for the Artinian Gorenstein algebra associated to the truncated matroid.