rssn 0.2.9

A comprehensive scientific computing library for Rust, aiming for feature parity with NumPy and SymPy.
Documentation 
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//! JSON-based FFI API for calculus of variations functions.

use std::os::raw::c_char;

use crate::ffi_apis::common::from_json_string;
use crate::ffi_apis::common::to_json_string;
use crate::symbolic::calculus_of_variations;
use crate::symbolic::core::Expr;

/// Computes the Euler-Lagrange equation using JSON.
#[unsafe(no_mangle)]
pub extern "C" fn rssn_json_euler_lagrange(
    lagrangian_json: *const c_char,
    func: *const c_char,
    var: *const c_char,
) -> *mut c_char {
    let lagrangian: Option<Expr> = from_json_string(lagrangian_json);

    let func_str = unsafe {
        if func.is_null() {
            None
        } else {
            std::ffi::CStr::from_ptr(func).to_str().ok()
        }
    };

    let var_str = unsafe {
        if var.is_null() {
            None
        } else {
            std::ffi::CStr::from_ptr(var).to_str().ok()
        }
    };

    match (lagrangian, func_str, var_str) {
        | (Some(l), Some(f), Some(v)) => {
            let result = calculus_of_variations::euler_lagrange(&l, f, v);

            to_json_string(&result)
        },
        | _ => std::ptr::null_mut(),
    }
}

/// Generates and attempts to solve the Euler-Lagrange equation using JSON.
#[unsafe(no_mangle)]
pub extern "C" fn rssn_json_solve_euler_lagrange(
    lagrangian_json: *const c_char,
    func: *const c_char,
    var: *const c_char,
) -> *mut c_char {
    let lagrangian: Option<Expr> = from_json_string(lagrangian_json);

    let func_str = unsafe {
        if func.is_null() {
            None
        } else {
            std::ffi::CStr::from_ptr(func).to_str().ok()
        }
    };

    let var_str = unsafe {
        if var.is_null() {
            None
        } else {
            std::ffi::CStr::from_ptr(var).to_str().ok()
        }
    };

    match (lagrangian, func_str, var_str) {
        | (Some(l), Some(f), Some(v)) => {
            let result = calculus_of_variations::solve_euler_lagrange(&l, f, v);

            to_json_string(&result)
        },
        | _ => std::ptr::null_mut(),
    }
}

/// Applies Hamilton's Principle using JSON.
#[unsafe(no_mangle)]
pub extern "C" fn rssn_json_hamiltons_principle(
    lagrangian_json: *const c_char,
    func: *const c_char,
    var: *const c_char,
) -> *mut c_char {
    let lagrangian: Option<Expr> = from_json_string(lagrangian_json);

    let func_str = unsafe {
        if func.is_null() {
            None
        } else {
            std::ffi::CStr::from_ptr(func).to_str().ok()
        }
    };

    let var_str = unsafe {
        if var.is_null() {
            None
        } else {
            std::ffi::CStr::from_ptr(var).to_str().ok()
        }
    };

    match (lagrangian, func_str, var_str) {
        | (Some(l), Some(f), Some(v)) => {
            let result = calculus_of_variations::hamiltons_principle(&l, f, v);

            to_json_string(&result)
        },
        | _ => std::ptr::null_mut(),
    }
}