Crank-Nicolson stability on a finite Dirichlet interval
= Crank-Nicolson stability on a finite Dirichlet interval
If $L$ is the negative semidefinite Dirichlet discrete Laplacian, the Crank-Nicolson amplification matrix
$$
Q=(I-\mu L/2)^{-1}(I+\mu L/2)
$$
has eigenvalues $(1+\mu\lambda_j/2)/(1-\mu\lambda_j/2)$ of modulus at most one for every $\mu\geq0$.