I have a little problem trying to calculate the eigenvalues of big symbolic (depending on $a$) Hessian matrices (28×28, 32×32 ...).
I think I've understand, by reading other posts, that Mathematica can not calculate the eigenvalues of such matrices since, I don't know why, it can not find the roots of the characteristic polynomial.
My goal is to find the lowest eigenvalue to see at which $a$ it vanishes. How could I do that since I don't have any idea at which $a$ it happens ? Thanks you