g descriptor of the exit status of the optimization.
iteration : int
    The number of iterations taken to solve the problem.

References
----------
.. [1] Dantzig, George B., Linear programming and extensions. Rand
       Corporation Research Study Princeton Univ. Press, Princeton, NJ,
       1963
.. [2] Hillier, S.H. and Lieberman, G.J. (1995), "Introduction to
       Mathematical Programming", McGraw-Hill, Chapter 4.
.. [3] Bland, Robert G. New finite pivoting rules for the simplex method.
       Mathematics of Operations Research (2), 1977: pp. 103-107.


Notes
-----
The expected problem formulation differs between the top level ``linprog``
module and the method specific solvers. The method specific solvers expect a
problem in standard form:

Minimize::

    c @ x

Subject to::

    A @ x == b
        x >= 0

Whereas the top level ``linprog`` module expects a problem of form:

Minimize::

    c @ x

Subject to::

    A_ub @ x <= b_ub
    A_eq @ x == b_eq
     lb <= x <= ub

where ``lb = 0`` and ``ub = None`` unless set in ``bounds``.

The original problem contains equality, upper-bound and variable constraints
whereas the method specific solver requires equality constraints and
variable non-negativity.

``linprog`` module converts the original problem to standard form by
converting the simple bounds to upper bound constraints, introducing
non-negative slack variables for inequality constraints, and expressing
unbounded variables as the difference between two non-negative variables.
r