The eigenvalues of A are λi=1−αμi, with μi being the
eigenvalues of ˆB. To find μi we note that the matrix elements of ˆB are
bij=2δij−δi+1j−δi−1j,
meaning that we
have the following set of eigenequations for component i(ˆBˆx)i=μixi,
resulting in
(ˆBˆx)i=n∑j=1(2δij−δi+1j−δi−1j)xj=2xi−xi+1−xi−1=μixi.