`atan2` seems to fire an error in debug mode

[yemine0x01]

Using this minimal example:

#include <cppad/cppad.hpp>
#include <iostream>
#include <vector>

int main()
{
    using CppAD::AD;

    const size_t nx = 3, ny = 1;
    CppAD::vector<AD<double>> ax(nx);
    std::cout << "Recording f(x0, x1, x2) = atan2(x1+x2, x0) ..." << std::endl;
    CppAD::Independent(ax);
    CppAD::vector<AD<double>> ay(ny);
    ay[0] = CppAD::atan2(ax[1] + ax[2], ax[0]);   // atan2(y=x1+x2, x=x0)
    CppAD::ADFun<double> fun(ax, ay);
    std::cout << "Recorded f(x0, x1, x2) = atan2(x1+x2, x0)." << std::endl;
    return 0;
}

compiling it in debug mode I have the following error:

Recording f(x0, x1, x2) = atan2(x1+x2, x0) ...
cppad-20260103 error from a known source:
A dependent variable value is not equal to its tape evaluation value,
perhaps it is nan.
Dependent variable value = -nan
Tape evaluation value    = -nan
Difference               = -nan

Error detected by false result for
    0
at line 528 in the file 
    /usr/local/include/cppad/core/fun_construct.hpp
mwe_debug: /usr/local/include/cppad/utility/error_handler.hpp:204: static void CppAD::ErrorHandler::Default(bool, int, const char*, const char*, const char*): Assertion `false' failed.
Aborted (core dumped)

But I don't know how to avoid it ?

[bradbell]

Adding the following statement directly after ax is created

std::cout << "ax = " << ax << "\n";

I get the following output (on my machine)

ax = { 0, 0, 0 }

so it is clear why the result is nan. You can fix this by changing the value of ax.

I you wish to store a function that has some components that are nan during recording, set the check_for_nan flag to false; see
https://cppad.readthedocs.io/latest/check_for_nan.html