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

to_json.cpp

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Convert an ADFun Object to a Json AD Graph: Example and Test

Source Code

# include <cppad/cppad.hpp>

bool to_json(void)
{  bool ok = true;
   using CppAD::vector;
   using CppAD::AD;
   //
   // An AD graph example
   // node_1 : x[0]
   // node_2 : x[1]
   // node_3 : x[0] + x[1]
   // node_4 : (x[0] + x[1]) * x[1]
   // y[0]   = (x[0] + x[1]) * x[1]
   // use single quote to avoid having to escape double quote
   std::string json =
      "{\n"
      "   'function_name'  : 'to_json example',\n"
      "   'op_define_vec'  : [ 2, [\n"
      "       { 'op_code':1, 'name':'add', 'n_arg':2 } ,\n"
      "       { 'op_code':2, 'name':'mul', 'n_arg':2 } ]\n"
      "   ],\n"
      "   'n_dynamic_ind'  : 0,\n"
      "   'n_variable_ind' : 2,\n"
      "   'constant_vec'   : [ 0, [ ] ],\n"
      "   'op_usage_vec'   : [ 2, [\n"
      "       [ 1, 1, 2 ] ,\n"
      "       [ 2, 3, 2 ] ]\n"
      "   ],\n"
      "   'dependent_vec' : [ 1, [4] ] \n"
      "}\n";
   // Convert the single quote to double quote
   for(size_t i = 0; i < json.size(); ++i)
      if( json[i] == '\'' ) json[i] = '"';
   //
   // f(x) = (x_0 + x_1) * x_1
   CppAD::ADFun< AD<double> > af;
   af.from_json(json);
   ok &= af.Domain() == 2;
   ok &= af.Range() == 1;
   //
   // Declare independent variables for a new recording
   vector< AD<double> > ax(2);
   ax[0] = 1.0;
   ax[1] = 2.0;
   CppAD::Independent(ax);
   //
   // Compute f(x)
   af.Forward(0, ax);
   //
   // Compute z = f'(x)
   vector< AD<double> > aw(1), az(2);
   aw[0] = 1.0;
   az    = af.Reverse(1, aw);
   //
   // define g(x) = f'(x)
   CppAD::ADFun<double> g(ax, az);
   // ------------------------------------------------------------------------
   // Convert to Json graph and back
   json = g.to_json();
   // std::cout << json;
   g.from_json(json);
   // ------------------------------------------------------------------------
   //
   // Evaluate function corresponding to g
   vector<double> x(2), z(2);
   x[0] = 3.0;
   x[1] = 4.0;
   z = g.Forward(0, x);
   //
   // should be derivative of f
   ok &= z[0] == x[1];
   ok &= z[1] == x[0] + 2.0 * x[1];
   //
   return ok;
}