Iterative solver for leastsquares problems.
lsmr solves the system of linear equations Ax = b. If the system is inconsistent, it solves the leastsquares problem min b  Ax_2. A is a rectangular matrix of dimension mbyn, where all cases are allowed: m = n, m > n, or m < n. B is a vector of length m. The matrix A may be dense or sparse (usually sparse).
New in version 0.11.0.
Parameters :  A : {matrix, sparse matrix, ndarray, LinearOperator}
b : (m,) ndarray
damp : float
atol, btol : float
conlim : float
maxiter : int
show : bool


Returns :  x : ndarray of float
istop : int
itn : int
normr : float
normar : float
norma : float
conda : float
normx : float

References
[R144]  D. C.L. Fong and M. A. Saunders, “LSMR: An iterative algorithm for sparse leastsquares problems”, SIAM J. Sci. Comput., vol. 33, pp. 29502971, 2011. http://arxiv.org/abs/1006.0758 
[R145]  LSMR Software, http://www.stanford.edu/~clfong/lsmr.html 