 and Nicholas J. Higham (2011)
       "Computing the Action of the Matrix Exponential,
       with an Application to Exponential Integrators."
       SIAM Journal on Scientific Computing,
       33 (2). pp. 488-511. ISSN 1064-8275
       http://eprints.ma.man.ac.uk/1591/

.. [2] Nicholas J. Higham and Awad H. Al-Mohy (2010)
       "Computing Matrix Functions."
       Acta Numerica,
       19. 159-208. ISSN 0962-4929
       http://eprints.ma.man.ac.uk/1451/

Examples
--------
>>> import numpy as np
>>> from scipy.sparse import csc_array
>>> from scipy.sparse.linalg import expm, expm_multiply
>>> A = csc_array([[1, 0], [0, 1]])
>>> A.toarray()
array([[1, 0],
       [0, 1]], dtype=int64)
>>> B = np.array([np.exp(-1.), np.exp(-2.)])
>>> B
array([ 0.36787944,  0.13533528])
>>> expm_multiply(A, B, start=1, stop=2, num=3, endpoint=True)
array([[ 1.        ,  0.36787944],
       [ 1.64872127,  0.60653066],
       [ 2.71828183,  1.        ]])
>>> expm(A).dot(B)                  # Verify 1st timestep
array([ 1.        ,  0.36787944])
>>> expm(1.5*A).dot(B)              # Verify 2nd timestep
array([ 1.64872127,  0.60653066])
>>> expm(2*A).dot(B)                # Verify 3rd timestep
array([ 2.71828183,  1.        ])
c