# include <cppad/cppad.hpp>
namespace {
     struct tape_size { size_t n_var; size_t n_op; };

     template <class Vector> void fun(
          const std::string& options ,
          const Vector& x, Vector& y, tape_size& before, tape_size& after
     )
     {     typedef typename Vector::value_type scalar;

          // phantom variable with index 0 and independent variables
          // begin operator, independent variable operators and end operator
          before.n_var = 1 + x.size(); before.n_op  = 2 + x.size();
          after.n_var  = 1 + x.size(); after.n_op   = 2 + x.size();

          // Create a variable that is is only used in the comparision operation
          // It is not used when the comparison operator is not included
          scalar one = 1. / x[0];
          before.n_var += 1; before.n_op += 1;
          after.n_var  += 0; after.n_op  += 0;
          // If we keep comparision operators, we must compute their operands
          if( options.find("no_compare_op") == std::string::npos )
          {     after.n_var += 1;  after.n_op += 1;
          }

          // Create a variable that is used by the result
          scalar two = x[0] * 5.;
          before.n_var += 1; before.n_op += 1;
          after.n_var  += 1; after.n_op += 1;

          // Only one variable created for this comparison operation
          // but the value depends on which branch is taken.
          scalar three;
          if( one < x[0] )        // comparison operator
               three = two / 2.0;  // division operator
          else
               three = 2.0 * two;  // multiplication operator
          // comparison and either division of multiplication operator
          before.n_var += 1; before.n_op += 2;
          // comparison operator depends on optimization options
          after.n_var += 1;  after.n_op += 1;
          // check if we are keeping the comparison operator
          if( options.find("no_compare_op") == std::string::npos )
               after.n_op += 1;

          // results for this operation sequence
          y[0] = three;
          before.n_var += 0; before.n_op  += 0;
          after.n_var  += 0; after.n_op   += 0;
     }
}

bool compare_op(void)
{     bool ok = true;
     using CppAD::AD;
     using CppAD::NearEqual;
     double eps10 = 10.0 * std::numeric_limits<double>::epsilon();

     // domain space vector
     size_t n  = 1;
     CPPAD_TESTVECTOR(AD<double>) ax(n);
     ax[0] = 0.5;

     // range space vector
     size_t m = 1;
     CPPAD_TESTVECTOR(AD<double>) ay(m);

     for(size_t k = 0; k < 2; k++)
     {     // optimization options
          std::string options = "";
          if( k == 0 )
               options = "no_compare_op";

          // declare independent variables and start tape recording
          CppAD::Independent(ax);

          // compute function value
          tape_size before, after;
          fun(options, ax, ay, before, after);

          // create f: x -> y and stop tape recording
          CppAD::ADFun<double> f(ax, ay);
          ok &= f.size_var() == before.n_var;
          ok &= f.size_op() == before.n_op;

          // Optimize the operation sequence
          f.optimize(options);
          ok &= f.size_var() == after.n_var;
          ok &= f.size_op() == after.n_op;

          // Check result for a zero order calculation for a different x,
          // where the result of the comparison is he same.
          CPPAD_TESTVECTOR(double) x(n), y(m), check(m);
          x[0] = 0.75;
          y    = f.Forward(0, x);
          if ( options == "" )
               ok  &= f.compare_change_number() == 0;
          fun(options, x, check, before, after);
          ok &= NearEqual(y[0], check[0], eps10, eps10);

          // Check case where result of the comparision is differnent
          // (hence one needs to re-tape to get correct result)
          x[0] = 2.0;
          y    = f.Forward(0, x);
          if ( options == "" )
               ok  &= f.compare_change_number() == 1;
          fun(options, x, check, before, after);
          ok  &= std::fabs(y[0] - check[0]) > 0.5;
     }
     return ok;
}