Task: Orbital elements
C++: #include <iostream>
#include <tuple>

class Vector {
private:
    double _x, _y, _z;

public:
    Vector(double x, double y, double z) : _x(x), _y(y), _z(z) {
        
    }

    double getX() {
        return _x;
    }

    double getY() {
        return _y;
    }

    double getZ() {
        return _z;
    }

    double abs() {
        return sqrt(_x * _x + _y * _y + _z * _z);
    }

    Vector operator+(const Vector& rhs) const {
        return Vector(_x + rhs._x, _y + rhs._y, _z + rhs._z);
    }

    Vector operator*(double m) const {
        return Vector(_x * m, _y * m, _z * m);
    }

    Vector operator/(double m) const {
        return Vector(_x / m, _y / m, _z / m);
    }

    friend std::ostream& operator<<(std::ostream& os, const Vector& v);
};

std::ostream& operator<<(std::ostream& os, const Vector& v) {
    return os << '(' << v._x << ", " << v._y << ", " << v._z << ')';
}

std::pair<Vector, Vector> orbitalStateVectors(
    double semiMajorAxis,
    double eccentricity,
    double inclination,
    double longitudeOfAscendingNode,
    double argumentOfPeriapsis,
    double trueAnomaly
) {
    auto mulAdd = [](const Vector& v1, double x1, const Vector& v2, double x2) {
        return v1 * x1 + v2 * x2;
    };

    auto rotate = [mulAdd](const Vector& iv, const Vector& jv, double alpha) {
        return std::make_pair(
            mulAdd(iv, +cos(alpha), jv, sin(alpha)),
            mulAdd(iv, -sin(alpha), jv, cos(alpha))
        );
    };

    Vector i(1, 0, 0);
    Vector j(0, 1, 0);
    Vector k(0, 0, 1);

    auto p = rotate(i, j, longitudeOfAscendingNode);
    i = p.first; j = p.second;
    p = rotate(j, k, inclination);
    j = p.first;
    p = rotate(i, j, argumentOfPeriapsis);
    i = p.first; j = p.second;

    auto l = semiMajorAxis * ((eccentricity == 1.0) ? 2.0 : (1.0 - eccentricity * eccentricity));
    auto c = cos(trueAnomaly);
    auto s = sin(trueAnomaly);
    auto r = l / (1.0 + eccentricity * c);;
    auto rprime = s * r * r / l;
    auto position = mulAdd(i, c, j, s) * r;
    auto speed = mulAdd(i, rprime * c - r * s, j, rprime * s + r * c);
    speed = speed / speed.abs();
    speed = speed * sqrt(2.0 / r - 1.0 / semiMajorAxis);

    return std::make_pair(position, speed);
}

int main() {
    auto res = orbitalStateVectors(1.0, 0.1, 0.0, 355.0 / (113.0 * 6.0), 0.0, 0.0);
    std::cout << "Position : " << res.first << '\n';
    std::cout << "Speed    : " << res.second << '\n';

    return 0;
}

Go: package main

import (
    "fmt"
    "math"
)

type vector struct{ x, y, z float64 }

func (v vector) add(w vector) vector {
    return vector{v.x + w.x, v.y + w.y, v.z + w.z}
}

func (v vector) mul(m float64) vector {
    return vector{v.x * m, v.y * m, v.z * m}
}

func (v vector) div(d float64) vector {
    return v.mul(1.0 / d)
}

func (v vector) abs() float64 {
    return math.Sqrt(v.x*v.x + v.y*v.y + v.z*v.z)
}

func (v vector) String() string {
    return fmt.Sprintf("(%g, %g, %g)", v.x, v.y, v.z)
}

func orbitalStateVectors(
    semimajorAxis, eccentricity, inclination, longitudeOfAscendingNode,
    argumentOfPeriapsis, trueAnomaly float64) (position vector, speed vector) {

    i := vector{1, 0, 0}
    j := vector{0, 1, 0}
    k := vector{0, 0, 1}

    mulAdd := func(v1, v2 vector, x1, x2 float64) vector {
        return v1.mul(x1).add(v2.mul(x2))
    }

    rotate := func(i, j vector, alpha float64) (vector, vector) {
        return mulAdd(i, j, math.Cos(alpha), math.Sin(alpha)),
            mulAdd(i, j, -math.Sin(alpha), math.Cos(alpha))
    }

    i, j = rotate(i, j, longitudeOfAscendingNode)
    j, _ = rotate(j, k, inclination)
    i, j = rotate(i, j, argumentOfPeriapsis)

    l := 2.0
    if eccentricity != 1.0 {
        l = 1.0 - eccentricity*eccentricity
    }
    l *= semimajorAxis
    c := math.Cos(trueAnomaly)
    s := math.Sin(trueAnomaly)
    r := l / (1.0 + eccentricity*c)
    rprime := s * r * r / l
    position = mulAdd(i, j, c, s).mul(r)
    speed = mulAdd(i, j, rprime*c-r*s, rprime*s+r*c)
    speed = speed.div(speed.abs())
    speed = speed.mul(math.Sqrt(2.0/r - 1.0/semimajorAxis))
    return
}

func main() {
    long := 355.0 / (113.0 * 6.0)
    position, speed := orbitalStateVectors(1.0, 0.1, 0.0, long, 0.0, 0.0)
    fmt.Println("Position :", position)
    fmt.Println("Speed    :", speed)
}