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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 .
AD Compound Assignment Addition: Example and Test
# include <cppad/cppad.hpp>

bool AddEq(void)
{   bool ok = true;
    using CppAD::AD;
    using CppAD::NearEqual;
    double eps99 = 99.0 * std::numeric_limits<double>::epsilon();

    // domain space vector
    size_t  n = 1;
    double x0 = .5;
    CPPAD_TESTVECTOR(AD<double>) x(n);
    x[0]      = x0;

    // declare independent variables and start tape recording
    CppAD::Independent(x);

    // range space vector
    size_t m = 2;
    CPPAD_TESTVECTOR(AD<double>) y(m);
    y[0] = x[0];         // initial value
    y[0] += 2;           // AD<double> += int
    y[0] += 4.;          // AD<double> += double
    y[1] = y[0] += x[0]; // use the result of a compound assignment

    // create f: x -> y and stop tape recording
    CppAD::ADFun<double> f(x, y);

    // check value
    ok &= NearEqual(y[0] , x0+2.+4.+x0, eps99, eps99);
    ok &= NearEqual(y[1] ,        y[0], eps99, eps99);

    // forward computation of partials w.r.t. x[0]
    CPPAD_TESTVECTOR(double) dx(n);
    CPPAD_TESTVECTOR(double) dy(m);
    dx[0] = 1.;
    dy    = f.Forward(1, dx);
    ok   &= NearEqual(dy[0], 2., eps99, eps99);
    ok   &= NearEqual(dy[1], 2., eps99, eps99);

    // reverse computation of derivative of y[0]
    CPPAD_TESTVECTOR(double)  w(m);
    CPPAD_TESTVECTOR(double) dw(n);
    w[0]  = 1.;
    w[1]  = 0.;
    dw    = f.Reverse(1, w);
    ok   &= NearEqual(dw[0], 2., eps99, eps99);

    // use a VecAD<Base>::reference object with computed addition
    CppAD::VecAD<double> v(1);
    AD<double> zero(0);
    AD<double> result = 1;
    v[zero] = 2;
    result += v[zero];
    ok     &= (result == 3);

    return ok;
}
Input File: example/general/add_eq.cpp