# SimPEG.utils.inverse_2x2_block_diagonal#

SimPEG.utils.inverse_2x2_block_diagonal(a11, a12, a21, a22, return_matrix=True, **kwargs)[source]#

Invert a set of 2x2 matricies from vectors containing their elements.

Parameters
a11, a12, a21, a22(n_blocks) numpy.ndarray

All arguments a11, a12, a21, a22 are vectors which contain the corresponding element for all 2x2 matricies

return_matrixbool, optional
• True: Returns the sparse block 2x2 matrix M.

• False: Returns the vectors containing the elements of each matrix’ inverse.

Returns
(2 * n_blocks, 2 * n_blocks) scipy.sparse.coo_matrix or list of (n_blocks) numpy.ndarray

If return_matrix = False, the function will return vectors b11, b12, b21, b22. If return_matrix = True, the function will return the block matrix M

Notes

The elements of a 2x2 matrix A are given by:

$\begin{split}A = \begin{bmatrix} a_{11} & a_{12} \\ a_{21} & a_{22} \end{bmatrix}\end{split}$

For a set of 2x2 matricies, the elements may be stored in a set of 4 distinct vectors $$\mathbf{a_{11}}$$, $$\mathbf{a_{12}}$$, $$\mathbf{a_{21}}$$ and $$\mathbf{a_{22}}$$. For each matrix, inverse_2x2_block_diagonal ouputs the vectors containing the elements of each matrix’ inverse; i.e. $$\mathbf{b_{11}}$$, $$\mathbf{b_{12}}$$, $$\mathbf{b_{21}}$$ and $$\mathbf{b_{22}}$$ where:

$\begin{split}A^{-1} = B = \begin{bmatrix} b_{11} & b_{12} \\ b_{21} & b_{22} \end{bmatrix}\end{split}$

For special applications, we may want to output the elements of the inverses of the matricies as a 2x2 block matrix of the form:

$\begin{split}M = \begin{bmatrix} D_{11} & D_{12} \\ D_{21} & D_{22} \end{bmatrix}\end{split}$

where $$D_{ij}$$ are diagonal matrices whose non-zero elements are defined by vector $$\mathbf{b_{ij}}$$. Where n is the number of matricies, the block matrix is sparse with dimensions (2n, 2n).

Examples