1. The problem statement, all variables and given/known data det(K-lambdaM)=0 K is stiffness and M is mass matrix 2. Relevant equations How do I make sure that Q'*M*Q=I Where Q is the matrix whose column entries are the eigen vectors. 3. The attempt at a solution I want to know how to do it without matlab help. Is it always true that I will get a diagonal matrix?