how to write c++ functions that accept numpy arrays with custom numeric types exposed via EigenPy

[ofloveandhate]

I'm looking for a bit of help.

I have C++ functions that accept Eigen vectors and matrices. And those functions are exposed to Python via Boost.Python, as are my numeric types, and I have exposed Eigen containers of my numeric types via EigenPy. So I think this is an eigenpy question.

But I'm struggling to provide inter-operability between the Eigen vectors for C++ calls and numpy containers with dtype my custom numeric type.

Do you have examples in eigenpy or pinnochio of a C++ function accepting Eigen data, but which when exposed to Python accepts numpy?

---

super cut-down example code

// in C++
def foo(Eigen::Vector v){
}

foo(Eigen::Vector(blabla))

# in Python

foo(np.array( [N(1), N(2), N(3) ])

where N is my wrapped custom numeric type.

But the call in Python fails because the C++ function expects an Eigen container, but it's getting a numpy container.

My specific error message:

Traceback (most recent call last):
  File "/Users/amethyst/github_repos/b2/python/test/tracking/amptracking_test.py", line 133, in test_tracker_quad
    tracker.track_path(y_end, t_start, t_end, y_start);
Boost.Python.ArgumentError: Python argument types in
    AMPTracker.track_path(AMPTracker, numpy.ndarray, Complex, Complex, numpy.ndarray)
did not match C++ signature:
    track_path(bertini::tracking::AMPTracker {lvalue}, Eigen::Matrix<boost::multiprecision::number<boost::multiprecision::backends::mpc_complex_backend<0u>, (boost::multiprecision::expression_template_option)1>, -1, 1, 0, -1, 1> {lvalue} result, boost::multiprecision::number<boost::multiprecision::backends::mpc_complex_backend<0u>, (boost::multiprecision::expression_template_option)1> start_time, boost::multiprecision::number<boost::multiprecision::backends::mpc_complex_backend<0u>, (boost::multiprecision::expression_template_option)1> end_time, Eigen::Matrix<boost::multiprecision::number<boost::multiprecision::backends::mpc_complex_backend<0u>, (boost::multiprecision::expression_template_option)1>, -1, 1, 0, -1, 1> start_point)

[ofloveandhate]

this SO post suggests copying in the data for the python --> c++ direction, but i dislike this. there should be a way to do it directly, to provide an overload / interoperability layer.

[ofloveandhate]

related open question, i think: https://stackoverflow.com/questions/76065711/converting-pyarray-to-eigenref-from-c

[ofloveandhate]

one more closely-related SO question, this time using eigency (but sadly not eigenpy)

[jcarpent]

Please look at this test

eigenpy/unittest/user_type.cpp

Lines 134 to 138 in e945a06

	template <typename Scalar>
	void print(const Eigen::Matrix<CustomType<Scalar>, Eigen::Dynamic,
	Eigen::Dynamic>& mat) {
	std::cout << mat << std::endl;
	}