lu_factor

LU Factorisation wrapper of:

\[LU = (\sigma \mathbf{I} - \mathbf{A})\]

In the case of A being a sparse matrix, the sparse methods in scipy are employed

param sigma:

Expansion frequency

type sigma:

float

param A:

Dynamics matrix

type A:

csc_matrix or np.ndarray

returns:

tuple (dense) or SuperLU (sparse) objects containing the LU factorisation

rtype:

tuple or SuperLU