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Questions related to the spectrum of graphs, defined using one of the possible variants of the discrete Laplace operator or Laplacian matrix. See https://en.wikipedia.org/wiki/Discrete_Laplace_operator

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Minimum negative eigenvalue of zero-one matrices

I wish to discuss or clarify here the answers given previously. Christian's answer fails to work for non-symmetric matrices, because then the inequality $\lambda_+\ge\frac Nn$ is deadly false. Take f …
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15 votes
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Eigenvalues of the complement of a graph

Edit (bis). There are two answers, depending on whether loops about vertices are allowed or not. In addition, the case of regular graphs is completely described. If loops are allowed The relation be …
Denis Serre's user avatar
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9 votes
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Are there good ways of relating a minor to the full determinant?

yes, there is the Sherman-Morrison formula $$\det B=(\det A)(b-yA^{-1}x),$$ where $b, x$ and $y$ are blocks: $$B=\begin{pmatrix} A & x \\ y & b \end{pmatrix}.$$ Edit. After Hachino's comment, one can …
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