Matrix exponential using scaled-squared subdiagonal Pade

Computes the matrix exponential or its action on a vector

sexpm(A) computes the matrix exponential of a square matrix A. sexpmv(A,b) computes the action of the matrix exponential on a given vector b. The codes can be much more efficient than MATLAB's standard expm if the matrix has eigenvalues of widely varying real part, and the rightmost eigenvalues do not have widely varying imaginary parts.
Details of the algorithm are described in
Stefan Guettel and Yuji Nakatsukasa, Scaled and squared subdiagonal Pade approximation for the matrix exponential, pdf, SIAM Journal on Matrix Analysis and Applications, Vol. 37(1), pp. 145-170, 2016.