`scipy.sparse.linalg._onenormest:_algorithm_2_2`

source: /scipy/sparse/linalg/_onenormest.py :221

Signature

def _algorithm_2_2 ( A , AT , t )

Summary

This is Algorithm 2.2.

Parameters

A : ndarray or other linear operator: A linear operator that can produce matrix products.
AT : ndarray or other linear operator: The transpose of A.
t : int, optional: A positive parameter controlling the tradeoff between accuracy versus time and memory usage.

Returns

g : sequence: A non-negative decreasing vector such that g[j] is a lower bound for the 1-norm of the column of A of jth largest 1-norm. The first entry of this vector is therefore a lower bound on the 1-norm of the linear operator A. This sequence has length t.
ind : sequence: The ith entry of ind is the index of the column A whose 1-norm is given by g[i]. This sequence of indices has length t, and its entries are chosen from range(n), possibly with repetition, where n is the order of the operator A.

Notes

This algorithm is mainly for testing. It uses the 'ind' array in a way that is similar to its usage in algorithm 2.4. This algorithm 2.2 may be easier to test, so it gives a chance of uncovering bugs related to indexing which could have propagated less noticeably to algorithm 2.4.

Aliases

scipy.sparse.linalg._onenormest._algorithm_2_2