d2/de5/Example_11_External_function_user_data.html

#include <codi.hpp>

#include <iostream>


using Real = codi::RealReverse;

using Tape = typename Real::Tape;

using Identifier = typename Real::Identifier;

using RealBase = typename Real::Real;


Real func(const Real& x) {

  return x * x * x;

}


void extFunc_rev(Tape* t, void* d, codi::VectorAccessInterface<typename Tape::Real, Identifier>* va) {

  codi::ExternalFunctionUserData* data = (codi::ExternalFunctionUserData*)d;


  // Step 4: Get data in the same order as it was added.

  Identifier t_i = data->getData<int>();

  double scale = data->getData<double>();


  Real t_b = va->getAdjoint(t_i, 0);


  std::cout << " Reverse: t_b = " << t_b  << ", scale = " << scale << std::endl;

}


void extFunc_del(Tape* t, void* d) {

  codi::ExternalFunctionUserData* data = (codi::ExternalFunctionUserData*)d;


  // Step 5: Delete the data

  delete data;


  std::cout << " Reset: data is deleted." <<  std::endl;

}


int main(int nargs, char** args) {

  Real x = 4.0;


  Tape& tape = Real::getTape();

  tape.setActive();


  tape.registerInput(x);

  Real t = func(x);


  codi::ExternalFunctionUserData* data = new codi::ExternalFunctionUserData();  // Step 1: Create the data object

  data->addData(t.getIdentifier());                                  // Step 2: Add data

  data->addData(0.01);


  // Step 3: Add the external function with the data

  tape.pushExternalFunction(codi::ExternalFunction<Tape>::create(extFunc_rev, data, extFunc_del));


  Real y = func(t);

  tape.registerOutput(y);


  tape.setPassive();

  y.setGradient(1.0);

  tape.evaluate();


  std::cout << "f(f(4.0)) = " << y << std::endl;

  std::cout << "d(f ○ f)/dx(4.0) = " << x.getGradient() << std::endl;


  tape.reset();


  return 0;

}