simple fortran-cpp-python prototype

[mahf708]

the idea here is:

Since AI models are usually written in Python, we can easily bridge our coupler infrastructure in F90 via a lightweight C++ bridge to call these models. This example illustrates the basic idea from a fortran_main through python_bridge to a python_main that calls python_torch. We hide the python_torch deps in main so that the C++ bridge doesn't need to know anything about them. We pass around pointers so that we don't copy data. Pytorch (not Python) can transfer the data (usually arrays) to GPU if it wants --- not shown here (yet)

todo:

• add docs (something to try at home as well as something to try on pm-gpu)
• add optional explicit gpu sync via pytorch device stuff
• explore dlpack for seamlessly wrapping of device/host data (say if we want ace on gpu to interface with omega on gpu, etc.)

[Copilot]

Pull Request Overview

This PR introduces a new prototype demonstrating interoperability between Fortran, C++, and Python with PyTorch integration. The implementation establishes a complete pipeline where Fortran initiates computation, C++ provides a bridge layer using pybind11, and Python performs PyTorch tensor operations.

Key changes:

• Creates a multi-language bridge architecture enabling Fortran → C++ → Python communication
• Implements PyTorch tensor operations callable from Fortran via C++ bridge
• Configures CMake build system with pybind11 integration for the prototype

Reviewed Changes

Copilot reviewed 6 out of 7 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
prototypes/fortran-cpp-python/src/python/python_torch.py	Implements PyTorch tensor sum operation
prototypes/fortran-cpp-python/src/python/python_main.py	Provides Python dispatcher entry point with lazy import
prototypes/fortran-cpp-python/src/fortran/fortran_main.f90	Fortran main program that initializes and calls Python operations
prototypes/fortran-cpp-python/src/cpp/python_bridge.hpp	C API header for Python bridge functions
prototypes/fortran-cpp-python/src/cpp/python_bridge.cpp	C++ implementation of Python bridge using pybind11
prototypes/fortran-cpp-python/CMakeLists.txt	CMake configuration for building the prototype
.gitignore	Ignores build artifacts and Python cache files

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[Copilot]

[nitpick] Comment text should be capitalized and properly formatted. 'we' should be 'We' and 'cpp' should be 'C++'.

Suggested change

	# we are importing here so we don't need to make the
	# cpp bridge aware of this stuff and such
	# We are importing here so we don't need to make the
	# C++ bridge aware of this stuff and such

[Copilot]

No validation is performed on the 'size' parameter before creating the array. If a negative or excessively large size is passed, it could lead to undefined behavior or security issues. Add validation to ensure size is positive and within reasonable bounds.

[Copilot]

The 'data' pointer is not validated for null before being passed to py::array_t constructor. Add a null check to prevent potential crashes or undefined behavior.

Suggested change

	if (data == nullptr) {
	std::cerr << "[C++] Error: data pointer is null." << std::endl;
	return -1;
	}

[Copilot]

The 'result' pointer is not validated for null before dereferencing at line 56. Add a null check to prevent potential crashes.

Suggested change

	if (result == nullptr) {
	std::cerr << "[C++] Error: result pointer is null." << std::endl;
	return -2;
	}