I have a big matrix with 8 by 8 and each of element is a polynomial function with regard to w. I need to calculate det[Matrix-identitymatrix], but since the large calculation, Mathematica cannot handle it, but actually, I only need the first coefficient of w in det[Matrix-identitymatrix], so I get rid of high power: Det[QM – IdentityMatrix] // Function[y, Normal[y + O[w]^2]]. but still cannot get the result after half hour, do I have any other option? Thanks, guys!