Module « scipy.linalg »

Fonction logm - module scipy.linalg

Signature de la fonction logm

def logm(A, disp=True) 

Description

logm.__doc__

    Compute matrix logarithm.

    The matrix logarithm is the inverse of
    expm: expm(logm(`A`)) == `A`

    Parameters
    ----------
    A : (N, N) array_like
        Matrix whose logarithm to evaluate
    disp : bool, optional
        Print warning if error in the result is estimated large
        instead of returning estimated error. (Default: True)

    Returns
    -------
    logm : (N, N) ndarray
        Matrix logarithm of `A`
    errest : float
        (if disp == False)

        1-norm of the estimated error, ||err||_1 / ||A||_1

    References
    ----------
    .. [1] Awad H. Al-Mohy and Nicholas J. Higham (2012)
           "Improved Inverse Scaling and Squaring Algorithms
           for the Matrix Logarithm."
           SIAM Journal on Scientific Computing, 34 (4). C152-C169.
           ISSN 1095-7197

    .. [2] Nicholas J. Higham (2008)
           "Functions of Matrices: Theory and Computation"
           ISBN 978-0-898716-46-7

    .. [3] Nicholas J. Higham and Lijing lin (2011)
           "A Schur-Pade Algorithm for Fractional Powers of a Matrix."
           SIAM Journal on Matrix Analysis and Applications,
           32 (3). pp. 1056-1078. ISSN 0895-4798

    Examples
    --------
    >>> from scipy.linalg import logm, expm
    >>> a = np.array([[1.0, 3.0], [1.0, 4.0]])
    >>> b = logm(a)
    >>> b
    array([[-1.02571087,  2.05142174],
           [ 0.68380725,  1.02571087]])
    >>> expm(b)         # Verify expm(logm(a)) returns a
    array([[ 1.,  3.],
           [ 1.,  4.]])