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

json_discrete_op.cpp

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Json add Operator: Example and Test

Source Code

# include <cppad/cppad.hpp>

namespace {
   double heaviside(const double &x)
   {  if( x < 0.0 )
         return 0.0;
      if( x == 0.0 )
         return 0.5;
      return 1.0;
   }
   CPPAD_DISCRETE_FUNCTION(double, heaviside)
}

bool discrete_op(void)
{  bool ok = true;
   using CppAD::vector;
   using CppAD::AD;
   //
   // The discrete function does not exist until its AD version is called
   heaviside( CppAD::AD<double>( 0.0 ) );
   //
   //
   // AD graph example
   // node_1 : p[0]
   // node_2 : x[0]
   // node_3 : heaviside(p[0])
   // node_4 : heaviside(p[1])
   // node_5 = heaviside(p[0]) + heaviside(p[1])
   // y[0]   = heaviside(p[0]) + heaviside(p[1])
   // use single quote to avoid having to escape double quote
   std::string json =
      "{\n"
      "   'function_name'  : 'discrete_op example',\n"
      "   'op_define_vec'  : [ 2, [\n"
      "       { 'op_code':1, 'name':'add',      'n_arg':2 } ,\n"
      "       { 'op_code':2, 'name':'discrete' }            ]\n"
      "   ],\n"
      "   'n_dynamic_ind'  : 1,\n"
      "   'n_variable_ind' : 1,\n"
      "   'constant_vec'   : [ 0, [ ] ],\n"
      "   'op_usage_vec'   : [ 3, [\n"
      "       [ 2, 'heaviside', 1, 1, [ 1 ] ] ,\n" // heaviside(p[0])
      "       [ 2, 'heaviside', 1, 1, [ 2 ] ] ,\n" // heaviside(x[0])
      "       [ 1, 3, 4 ] ]\n"  // heaviside(p[0]) + heaviside(x[0])
      "   ],\n"
      "   'dependent_vec' : [ 1, [5] ] \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, p) = x_0 + ( p_0 + p_1 )
   CppAD::ADFun<double> f;
   f.from_json(json);
   ok &= f.Domain() == 1;
   ok &= f.Range() == 1;
   ok &= f.size_dyn_ind() == 1;
   //
   // set independent variables and parameters
   CPPAD_TESTVECTOR(double) p(1), x(1);
   p[0] = 0.0;
   x[0] = 2.0;
   //
   // compute y = f(x, p)
   f.new_dynamic(p);
   CPPAD_TESTVECTOR(double) y = f.Forward(0, x);
   //
   // check result
   ok &= y[0] == heaviside(p[0]) + heaviside(x[0]);
   // -----------------------------------------------------------------------
   // Convert to Json graph and back again
   json = f.to_json();
   // std::cout << "json = " << json;
   f.from_json(json);
   // -----------------------------------------------------------------------
   ok &= f.Domain() == 1;
   ok &= f.Range() == 1;
   ok &= f.size_dyn_ind() == 1;
   //
   // set independent variables and parameters
   p[0] = -2.0;
   x[0] = 2.0;
   //
   // compute y = f(x, p)
   f.new_dynamic(p);
   y = f.Forward(0, x);
   //
   // check result
   ok &= y[0] == heaviside(p[0]) + heaviside(x[0]);
   //
   return ok;
}