scipy.sparse.linalg.expm_multiply¶

scipy.sparse.linalg.
expm_multiply
(A, B, start=None, stop=None, num=None, endpoint=None)[source]¶ Compute the action of the matrix exponential of A on B.
Parameters: A : transposable linear operator
The operator whose exponential is of interest.
B : ndarray
The matrix or vector to be multiplied by the matrix exponential of A.
start : scalar, optional
The starting time point of the sequence.
stop : scalar, optional
The end time point of the sequence, unless endpoint is set to False. In that case, the sequence consists of all but the last of
num + 1
evenly spaced time points, so that stop is excluded. Note that the step size changes when endpoint is False.num : int, optional
Number of time points to use.
endpoint : bool, optional
If True, stop is the last time point. Otherwise, it is not included.
Returns: expm_A_B : ndarray
The result of the action \(e^{t_k A} B\).
Notes
The optional arguments defining the sequence of evenly spaced time points are compatible with the arguments of
numpy.linspace
.The output ndarray shape is somewhat complicated so I explain it here. The ndim of the output could be either 1, 2, or 3. It would be 1 if you are computing the expm action on a single vector at a single time point. It would be 2 if you are computing the expm action on a vector at multiple time points, or if you are computing the expm action on a matrix at a single time point. It would be 3 if you want the action on a matrix with multiple columns at multiple time points. If multiple time points are requested, expm_A_B[0] will always be the action of the expm at the first time point, regardless of whether the action is on a vector or a matrix.
References
[R380] Awad H. AlMohy 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. 488511. ISSN 10648275 http://eprints.ma.man.ac.uk/1591/ [R381] Nicholas J. Higham and Awad H. AlMohy (2010) “Computing Matrix Functions.” Acta Numerica, 19. 159208. ISSN 09624929 http://eprints.ma.man.ac.uk/1451/ Examples
>>> from scipy.sparse import csc_matrix >>> from scipy.sparse.linalg import expm, expm_multiply >>> A = csc_matrix([[1, 0], [0, 1]]) >>> A.todense() matrix([[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. ])