// SPDX-License-Identifier: EPL-2.0 OR GPL-2.0-or-later
// SPDX-FileCopyrightText: Bradley M. Bell <bradbell@seanet.com>
// SPDX-FileContributor: 2003-22 Bradley M. Bell
// ----------------------------------------------------------------------------

/*
Two old SubEq examples now used just for valiadation testing
*/
# include <cppad/cppad.hpp>

namespace { // BEGIN empty namespace

bool SubEqTestOne(void)
{  bool ok = true;

   using namespace CppAD;

   // independent variable vector, indices, values, and declaration
   CPPAD_TESTVECTOR(AD<double>) U(2);
   size_t s = 0;
   size_t t = 1;
   U[s] = 3.;
   U[t] = 2.;
   Independent(U);

   // dependent variable vector and indices
   CPPAD_TESTVECTOR(AD<double>) Z(2);
   size_t x = 0;
   size_t y = 1;

   // dependent variable values
   Z[x]  = U[s];
   Z[y]  = U[t];
   Z[x] -= U[t];  // AD<double> -= AD<double>
   Z[y] -= 5.;    // AD<double> -= double

   // create f: U -> Z and vectors used for derivative calculations
   ADFun<double> f(U, Z);
   CPPAD_TESTVECTOR(double) v( f.Domain() );
   CPPAD_TESTVECTOR(double) w( f.Range() );

   // check function values
   ok &= ( Z[x] == 3. - 2. );
   ok &= ( Z[y] == 2. - 5. );

   // forward computation of partials w.r.t. t
   v[s] = 0.;
   v[t] = 1.;
   w = f.Forward(1, v);
   ok &= ( w[x] == -1. );  // dx/dt
   ok &= ( w[y] == 1. );   // dy/dt

   // reverse computation of second partials of x
   CPPAD_TESTVECTOR(double) r( f.Domain() * 2 );
   w[x] = 1.;
   w[y] = 0.;
   r = f.Reverse(2, w);
   ok &= ( r[2 * s + 1] == 0. );  // d^2 x / (ds ds)
   ok &= ( r[2 * t + 1] == 0. );  // d^2 x / (ds dt)

   return ok;
}

bool SubEqTestTwo(void)
{  bool ok = true;
   using namespace CppAD;
   double eps99 = 99.0 * std::numeric_limits<double>::epsilon();

   // independent variable vector
   double u0 = .5;
   CPPAD_TESTVECTOR(AD<double>) U(1);
   U[0]      = u0;
   Independent(U);

   // dependent variable vector
   CPPAD_TESTVECTOR(AD<double>) Z(1);
   Z[0] = U[0];       // initial value
   Z[0] -= 2;         // AD<double> -= int
   Z[0] -= 4.;        // AD<double> -= double
   Z[0] -= 2 * U[0];  // AD<double> -= AD<double>

   // create f: U -> Z and vectors used for derivative calculations
   ADFun<double> f(U, Z);
   CPPAD_TESTVECTOR(double) v(1);
   CPPAD_TESTVECTOR(double) w(1);

   // check value
   ok &= NearEqual(Z[0] , u0-2-4-2*u0,  eps99 , eps99);

   // forward computation of partials w.r.t. u
   size_t j;
   size_t p     = 5;
   double jfac  = 1.;
   double value = -1.;
   v[0]         = 1.;
   for(j = 1; j < p; j++)
   {  jfac *= double(j);
      w     = f.Forward(j, v);
      ok &= NearEqual(w[0], value/jfac, eps99, eps99); // d^jz/du^j
      v[0]  = 0.;
      value = 0.;
   }

   // reverse computation of partials of Taylor coefficients
   CPPAD_TESTVECTOR(double) r(p);
   w[0]  = 1.;
   r     = f.Reverse(p, w);
   jfac  = 1.;
   value = -1.;
   for(j = 0; j < p; j++)
   {  ok &= NearEqual(r[j], value/jfac, eps99, eps99); // d^jz/du^j
      jfac *= double(j + 1);
      value = 0.;
   }

   return ok;
}

} // END empty namespace

bool SubEq(void)
{  bool ok = true;
   ok &= SubEqTestOne();
   ok &= SubEqTestTwo();
   return ok;
}
