// SPDX-License-Identifier: EPL-2.0 OR GPL-2.0-or-later
// SPDX-FileCopyrightText: Bradley M. Bell <bradbell@seanet.com>
// SPDX-FileContributor: 2003-24 Bradley M. Bell
// ----------------------------------------------------------------------------
/*
{xrst_begin simplex_method.cpp}
{xrst_spell
   rlr
}

abs_normal simplex_method: Example and Test
###########################################

Problem
*******
Our original problem is

.. math::

   \R{minimize} \; | u - 1| \; \R{w.r.t} \; u \in \B{R}

We reformulate this as the following problem

.. math::

   \begin{array}{rlr}
      \R{minimize}      & v             & \R{w.r.t} \; (u,v) \in \B{R}^2 \\
      \R{subject \; to} &  u - 1 \leq v \\
                         &  1 - u \leq v
   \end{array}

We know that the value of :math:`v` at the solution is greater than
or equal zero. Hence we can reformulate this problem as

.. math::

   \begin{array}{rlr}
   \R{minimize}      & v             & \R{w.r.t} \; ( u_- , u_+ , v) \in \B{R}_+^3 \\
   \R{subject \; to} & u_+ - u_- - 1  \leq v \\
                     &  1 - u_+ + u_- \leq v
   \end{array}

This is equivalent to

.. math::

   \begin{array}{rlr}
      \R{minimize}
      & (0, 0, 1) \cdot ( u_+, u_- , v)^T  & \R{w.r.t} \; (u,v) \in \B{R}_+^3 \\
   \R{subject \; to}
      &
      \left( \begin{array}{ccc}
         +1 & -1 & -1 \\
         -1 & +1 & +1
      \end{array} \right)
      \left( \begin{array}{c} u_+ \\ u_- \\ v \end{array} \right)
      +
      \left( \begin{array}{c} -1 \\ 1 \end{array} \right)
      \leq
      0
   \end{array}

which is in the form expected by :ref:`simplex_method-name` .

Source
******
{xrst_literal
   // BEGIN C++
   // END C++
}

{xrst_end simplex_method.cpp}
*/
// BEGIN C++
# include <limits>
# include <cppad/utility/vector.hpp>
# include "simplex_method.hpp"

bool simplex_method(void)
{  bool ok = true;
   typedef CppAD::vector<double> vector;
   double eps99 = 99.0 * std::numeric_limits<double>::epsilon();
   //
   size_t n = 3;
   size_t m = 2;
   vector A(m * n), b(m), c(n), xout(n);
   A[ 0 * n + 0 ] =  1.0; // A(0,0)
   A[ 0 * n + 1 ] = -1.0; // A(0,1)
   A[ 0 * n + 2 ] = -1.0; // A(0,2)
   //
   A[ 1 * n + 0 ] = -1.0; // A(1,0)
   A[ 1 * n + 1 ] = +1.0; // A(1,1)
   A[ 1 * n + 2 ] = -1.0; // A(1,2)
   //
   b[0]           = -1.0;
   b[1]           =  1.0;
   //
   c[0]           =  0.0;
   c[1]           =  0.0;
   c[2]           =  1.0;
   //
   size_t maxitr  = 10;
   size_t level   = 0;
   //
   ok &= CppAD::simplex_method(level, A, b, c,  maxitr, xout);
   //
   // check optimal value for u
   ok &= std::fabs( xout[0] - 1.0 ) < eps99;
   //
   // check optimal value for v
   ok &= std::fabs( xout[1] ) < eps99;
   //
   return ok;
}
// END C++
