The matrix exponential exp(At) may be approximated to in some circumstances by the matrix function φ_p,q(At), where φ_p,q(u) is a Padé approximant to exp(u). The approximation breaks down if A has large latent roots, and in this case may be replaced by {φ_p,q(At/r)}^r for some integer r. An error analysis of the latter approximation is given. A reply from the original author follows.