Is a symmetric real matrix with diagonal entries strictly greater than $1$ and off-diagonal entries positive but strictly less than $1$ necessarily positive-semidefinite?
[Math] Positive symmetric matrices and positive-definiteness
linear algebramatricesoptimizationquadratic-forms
Best Answer
Nope. Just playing around with my computer, I found the matrix
[$\frac{11}{10}$ $\frac{1}{100}$ $\frac{99}{100}$]
[$\frac{1}{100}$ $\frac{11}{10}$ $\frac{99}{100}$]
[$\frac{99}{100}$ $\frac{99}{100}$ $\frac{11}{10}$]
with determinant $\frac{-25179}{31250}$.
Is this perhaps a misremembering of the definition of a diagonally dominant matrix?