\(\newcommand{\W}[1]{ \; #1 \; }\) \(\newcommand{\R}[1]{ {\rm #1} }\) \(\newcommand{\B}[1]{ {\bf #1} }\) \(\newcommand{\D}[2]{ \frac{\partial #1}{\partial #2} }\) \(\newcommand{\DD}[3]{ \frac{\partial^2 #1}{\partial #2 \partial #3} }\) \(\newcommand{\Dpow}[2]{ \frac{\partial^{#1}}{\partial {#2}^{#1}} }\) \(\newcommand{\dpow}[2]{ \frac{ {\rm d}^{#1}}{{\rm d}\, {#2}^{#1}} }\)

atomic_four_vector_neg.cpp

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Atomic Vector Negation Example

f(u, w)

For this example, \(f : \B{R}^{2m} \rightarrow \B{R}^m\) is defined by \(f(u, w) = u - w\). where u and w are in \(\B{R}^m\).

g(u, w)

For this example \(g : \B{R}^{2m} \rightarrow \B{R}^m\) is defined by \(g_i (u, w) = \partial_{w[i]} f_i (u, w)\)

Source

# include <cppad/cppad.hpp>
# include <cppad/example/atomic_four/vector/vector.hpp>
bool neg(void)
{  bool ok = true;
   using CppAD::NearEqual;
   using CppAD::AD;
   double eps99 = 99.0 * CppAD::numeric_limits<double>::epsilon();
   //
   // vec_op
   // atomic vector_op object
   CppAD::atomic_vector<double> vec_op("atomic_vector");
   //
   // m
   // size of u, v
   size_t m = 5;
   //
   // add_op, neg_op
   typedef CppAD::atomic_vector<double>::op_enum_t op_enum_t;
   op_enum_t add_op = CppAD::atomic_vector<double>::add_enum;
   op_enum_t neg_op = CppAD::atomic_vector<double>::neg_enum;
   // -----------------------------------------------------------------------
   // Record f(u, v) = u - v
   // -----------------------------------------------------------------------
   // Independent variable vector
   CPPAD_TESTVECTOR( CppAD::AD<double> ) auv(2 * m);
   for(size_t j = 0; j < 2 * m; ++j)
      auv[j] = AD<double>(1 + j);
   CppAD::Independent(auv);
   //
   // au, av
   CPPAD_TESTVECTOR( CppAD::AD<double> ) au(m), av(m);
   for(size_t i = 0; i < m; ++i)
   {  au[i] = auv[0 * m + i];
      av[i] = auv[1 * m + i];
   }
   //
   // ax = av
   CPPAD_TESTVECTOR( CppAD::AD<double> ) ax(m);
   for(size_t i = 0; i < m; ++i)
      ax[i] = av[i];
   //
   // ay = - av
   CPPAD_TESTVECTOR( CppAD::AD<double> ) ay(m);
   vec_op(neg_op, ax, ay);
   //
   // ax = (au, ay)
   ax.resize(2 * m);
   for(size_t i = 0; i < m; ++i)
   {  ax[i]     = au[i];
      ax[m + i] = ay[i];
   }
   //
   // az = au + ay
   CPPAD_TESTVECTOR( CppAD::AD<double> ) az(m);
   vec_op(add_op, ax, az);
   //
   // f
   CppAD::ADFun<double> f(auv, az);
   // -----------------------------------------------------------------------
   // check forward mode on f
   // -----------------------------------------------------------------------
   //
   // uv, duv
   CPPAD_TESTVECTOR(double) uv(2 * m), duv(2 * m);
   for(size_t j = 0; j < 2 * m; ++j)
   {  uv[j]  = double(1 + j);
      duv[j] = double(j);
   }
   //
   // z, dz
   CPPAD_TESTVECTOR(double) z(m), dz(m);
   z  = f.Forward(0, uv);
   dz = f.Forward(1, duv);
   //
   // ok
   for(size_t i = 0; i < m; ++i)
   {  double check_z  = uv[0 * m + i] - uv[1 * m + i];
      ok             &= NearEqual( z[i] ,  check_z,  eps99, eps99);
      double check_dz = double(0 * m + i) - double(1 * m + i);
      ok             &= NearEqual( dz[i] ,  check_dz,  eps99, eps99);
   }
   // -----------------------------------------------------------------------
   // Record g_i (u, v) = \partial d/dv[i] f_i (u , v)
   // -----------------------------------------------------------------------
   //
   // af
   CppAD::ADFun< AD<double>, double > af = f.base2ad();
   //
   // auv
   CppAD::Independent(auv);
   //
   // aduv
   CPPAD_TESTVECTOR( AD<double> ) aduv(2 * m);
   for(size_t i = 0; i < m; ++i)
   {  aduv[0 * m + i]  = 0.0; // du[i]
      aduv[1 * m + i]  = 1.0; // dv[i]
   }
   //
   // az
   // use the fact that d_v[i] f_k (u, v) is zero when i != k
   af.Forward(0, auv);
   az = af.Forward(1, aduv);
   CppAD::ADFun<double> g(auv, az);
   // -----------------------------------------------------------------------
   // check forward mode on g
   // -----------------------------------------------------------------------
   //
   // z
   z = g.Forward(0, uv);
   //
   // ok
   for(size_t i = 0; i < m; ++i)
   {  double check_z  = - 1.0;
      ok             &= NearEqual( z[i] ,  check_z,  eps99, eps99);
   }
   return ok;
}