scipy.sparse.linalg.eigs¶

scipy.sparse.linalg.
eigs
(A, k=6, M=None, sigma=None, which='LM', v0=None, ncv=None, maxiter=None, tol=0, return_eigenvectors=True, Minv=None, OPinv=None, OPpart=None)[source]¶ Find k eigenvalues and eigenvectors of the square matrix A.
Solves
A * x[i] = w[i] * x[i]
, the standard eigenvalue problem for w[i] eigenvalues with corresponding eigenvectors x[i].If M is specified, solves
A * x[i] = w[i] * M * x[i]
, the generalized eigenvalue problem for w[i] eigenvalues with corresponding eigenvectors x[i] Parameters
 Andarray, sparse matrix or LinearOperator
An array, sparse matrix, or LinearOperator representing the operation
A * x
, where A is a real or complex square matrix. kint, optional
The number of eigenvalues and eigenvectors desired. k must be smaller than N1. It is not possible to compute all eigenvectors of a matrix.
 Mndarray, sparse matrix or LinearOperator, optional
An array, sparse matrix, or LinearOperator representing the operation M*x for the generalized eigenvalue problem
A * x = w * M * x.
M must represent a real symmetric matrix if A is real, and must represent a complex Hermitian matrix if A is complex. For best results, the data type of M should be the same as that of A. Additionally:
If sigma is None, M is positive definite
If sigma is specified, M is positive semidefinite
If sigma is None, eigs requires an operator to compute the solution of the linear equation
M * x = b
. This is done internally via a (sparse) LU decomposition for an explicit matrix M, or via an iterative solver for a general linear operator. Alternatively, the user can supply the matrix or operator Minv, which givesx = Minv * b = M^1 * b
. sigmareal or complex, optional
Find eigenvalues near sigma using shiftinvert mode. This requires an operator to compute the solution of the linear system
[A  sigma * M] * x = b
, where M is the identity matrix if unspecified. This is computed internally via a (sparse) LU decomposition for explicit matrices A & M, or via an iterative solver if either A or M is a general linear operator. Alternatively, the user can supply the matrix or operator OPinv, which givesx = OPinv * b = [A  sigma * M]^1 * b
. For a real matrix A, shiftinvert can either be done in imaginary mode or real mode, specified by the parameter OPpart (‘r’ or ‘i’). Note that when sigma is specified, the keyword ‘which’ (below) refers to the shifted eigenvaluesw'[i]
where: If A is real and OPpart == ‘r’ (default),
w'[i] = 1/2 * [1/(w[i]sigma) + 1/(w[i]conj(sigma))]
. If A is real and OPpart == ‘i’,
w'[i] = 1/2i * [1/(w[i]sigma)  1/(w[i]conj(sigma))]
.
If A is complex,
w'[i] = 1/(w[i]sigma)
. v0ndarray, optional
Starting vector for iteration. Default: random
 ncvint, optional
The number of Lanczos vectors generated ncv must be greater than k; it is recommended that
ncv > 2*k
. Default:min(n, max(2*k + 1, 20))
 whichstr, [‘LM’  ‘SM’  ‘LR’  ‘SR’  ‘LI’  ‘SI’], optional
Which k eigenvectors and eigenvalues to find:
‘LM’ : largest magnitude
‘SM’ : smallest magnitude
‘LR’ : largest real part
‘SR’ : smallest real part
‘LI’ : largest imaginary part
‘SI’ : smallest imaginary part
When sigma != None, ‘which’ refers to the shifted eigenvalues w’[i] (see discussion in ‘sigma’, above). ARPACK is generally better at finding large values than small values. If small eigenvalues are desired, consider using shiftinvert mode for better performance.
 maxiterint, optional
Maximum number of Arnoldi update iterations allowed Default:
n*10
 tolfloat, optional
Relative accuracy for eigenvalues (stopping criterion) The default value of 0 implies machine precision.
 return_eigenvectorsbool, optional
Return eigenvectors (True) in addition to eigenvalues
 Minvndarray, sparse matrix or LinearOperator, optional
See notes in M, above.
 OPinvndarray, sparse matrix or LinearOperator, optional
See notes in sigma, above.
 OPpart{‘r’ or ‘i’}, optional
See notes in sigma, above
 Returns
 wndarray
Array of k eigenvalues.
 vndarray
An array of k eigenvectors.
v[:, i]
is the eigenvector corresponding to the eigenvalue w[i].
 Raises
 ArpackNoConvergence
When the requested convergence is not obtained. The currently converged eigenvalues and eigenvectors can be found as
eigenvalues
andeigenvectors
attributes of the exception object.
See also
Notes
This function is a wrapper to the ARPACK [1] SNEUPD, DNEUPD, CNEUPD, ZNEUPD, functions which use the Implicitly Restarted Arnoldi Method to find the eigenvalues and eigenvectors [2].
References
 1
ARPACK Software, http://www.caam.rice.edu/software/ARPACK/
 2
R. B. Lehoucq, D. C. Sorensen, and C. Yang, ARPACK USERS GUIDE: Solution of Large Scale Eigenvalue Problems by Implicitly Restarted Arnoldi Methods. SIAM, Philadelphia, PA, 1998.
Examples
Find 6 eigenvectors of the identity matrix:
>>> from scipy.sparse.linalg import eigs >>> id = np.eye(13) >>> vals, vecs = eigs(id, k=6) >>> vals array([ 1.+0.j, 1.+0.j, 1.+0.j, 1.+0.j, 1.+0.j, 1.+0.j]) >>> vecs.shape (13, 6)