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@(@\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}} }@)@This is cppad-20221105 documentation. Here is a link to its current documentation .
C++ AD Graph 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 std::string;
    //
    // 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])
    //
    // C++ graph object
    CppAD::cpp_graph graph_obj;
    //
    // operator being used
    CppAD::graph::graph_op_enum op_enum;
    //
    // set scalars
    graph_obj.function_name_set("discrete_op example");
    size_t n_dynamic_ind = 1;
    graph_obj.n_dynamic_ind_set(n_dynamic_ind);
    size_t n_variable_ind = 1;
    graph_obj.n_variable_ind_set(n_variable_ind);
    //
    // name_index corresponding to heaviside function
    size_t name_index = graph_obj.discrete_name_vec_size();
    graph_obj.discrete_name_vec_push_back("heaviside");
    //
    // heaviside(p[0])
    op_enum = CppAD::graph::discrete_graph_op;
    graph_obj.operator_vec_push_back(op_enum);
    graph_obj.operator_arg_push_back(name_index);  // name_index
    graph_obj.operator_arg_push_back(1);           // node arg
    //
    // heaviside(x[0])
    graph_obj.operator_vec_push_back(op_enum);
    graph_obj.operator_arg_push_back(name_index);  // name_index
    graph_obj.operator_arg_push_back(2);           // node arg
    //
    // heaviside(p[0]) + heaviside(x[0])
    op_enum = CppAD::graph::add_graph_op;
    graph_obj.operator_vec_push_back(op_enum);
    graph_obj.operator_arg_push_back(3);           // first node arg
    graph_obj.operator_arg_push_back(4);           // second node arg
    //
    // y[0] = heaviside(p[0]) + heaviside(x[0])
    graph_obj.dependent_vec_push_back(5);
    //
    // f(x, p) = heaviside(p[0]) + heaviside(x[0])
    CppAD::ADFun<double> f;
    f.from_graph(graph_obj);
    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 function to graph and back again
    f.to_graph(graph_obj);
    f.from_graph(graph_obj);
    // -----------------------------------------------------------------------
    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;
}

Input File: example/graph/discrete_op.cpp