divide.m

function x = divide(op,b,mode)
%\  Backslash or left matrix divide.
%
%   X = A\B is similar to Matlab's backslash operator, except that A
%   is always a Spot operator, and b is always a numeric column
%   vector. X is computed as the solution to the least-squares problem
%
%   (*)  minimize  ||Ax - b||_2.
%
%   The least-squares problem (*) is solved using LSQR with default
%   parameters specified by spotparams.
%
%   See also mldivide, opSpot.mrdivide, opFoG, opInverse, opPInverse, spotparams.

%   Copyright 2009, Ewout van den Berg and Michael P. Friedlander
%   See the file COPYING.txt for full copyright information.
%   Use the command 'spot.gpl' to locate this file.

%   http://www.cs.ubc.ca/labs/scl/spot
   
   if mode == 1
      A = op;
   else
      A = op';
   end
   [m,n] = size(A);
   opts = spotparams;
   maxits = opts.cgitsfact * min(m,min(n,20));
   x = spot.solvers.lsqr(m,n,A,b, ...
         opts.cgdamp,opts.cgtol,opts.cgtol,opts.conlim,maxits,opts.cgshow);