Basically I try to compute several smallest eigenvalues of some sparse 50k*50k eigenvalue problems using matlab.
$$Ax = \lambda Bx$$
With matlab eigs, it's not as fast as I expected. So I tried some preconditioned routine like lobpcg, however it said "The problem size is too small, relative to the block size. Try using eig or eigs instead".
Anyone can give some suggestion on how can I circumvent this with lobpcg or using some other routine?