/  Slash or right matrix divide.
 
    X = A/B is similar to Matlab's slash operator. If B is a Spot
    operator and A is a matrix then X is computed as the transpose
    of the solution to the least-squares problem
 
    (*)  minimize  ||B'x - A'||_F;
 
    when A is a vector, this is a standard least-squares problem.
 
    If B is a scalar and A is a spot operator, then X = opFoG(1/B,A).
 
    The least-squares problem (*) is solved using LSQR with default
    parameters specified by spotparams.