Hi there, I'm trying to simulate a vibrating plate with free edges. If i consider a consider a plate with fixed edges, the eigenvectors of the matrix bellow (which repesents the Laplacien operator) with S as a nxn tridiagonal matrix with -4 on the diagonal and 1s on either side (making the following a n2 by n2 matrix representing a plate with n2 points). correspond to the state of the plate (the following example is for a plate simulated by a 4 by 4 grid), so i can generate the following images. I found an article online (in french) which indicates that it is possible, using the same method but a different matrix to find the resonant states of a plate with free edges (Neumann conditions). My only question is how to build a matrix with such conditions? Has anyone encountered this problem before?