Compute the first few eigenvalues (by magnitude) and associated eigenvectors of a matrix.
get_first_eigs(some_mat, num_eigs)A list with two entries:
vals contains a length-num_eigs vector of the first few
eigenvalues,
and vects contains an nrow(some_mat) by num_eigs matrix
of the associated eigenvectors.
Matrix for which eigenvalues and eigenvectors are to be calculated.
Number of eigenvalues and eigenvectors to calculate.