Task: Orbital elements
C#: using System;

namespace OrbitalElements {
    class Vector {
        public Vector(double x, double y, double z) {
            X = x;
            Y = y;
            Z = z;
        }

        public double X { get; set; }
        public double Y { get; set; }
        public double Z { get; set; }

        public double Abs() {
            return Math.Sqrt(X * X + Y * Y + Z * Z);
        }

        public static Vector operator +(Vector lhs, Vector rhs) {
            return new Vector(lhs.X + rhs.X, lhs.Y + rhs.Y, lhs.Z + rhs.Z);
        }

        public static Vector operator *(Vector self, double m) {
            return new Vector(self.X * m, self.Y * m, self.Z * m);
        }

        public static Vector operator /(Vector self, double m) {
            return new Vector(self.X / m, self.Y / m, self.Z / m);
        }

        public override string ToString() {
            return string.Format("({0}, {1}, {2})", X, Y, Z);
        }
    }

    class Program {
        static Tuple<Vector, Vector> OrbitalStateVectors(
            double semiMajorAxis,
            double eccentricity,
            double inclination,
            double longitudeOfAscendingNode,
            double argumentOfPeriapsis,
            double trueAnomaly
        ) {
            Vector mulAdd(Vector v1, double x1, Vector v2, double x2) {
                return v1 * x1 + v2 * x2;
            }

            Tuple<Vector, Vector> rotate(Vector iv, Vector jv, double alpha) {
                return new Tuple<Vector, Vector>(
                    mulAdd(iv, +Math.Cos(alpha), jv, Math.Sin(alpha)),
                    mulAdd(iv, -Math.Sin(alpha), jv, Math.Cos(alpha))
                );
            }

            var i = new Vector(1, 0, 0);
            var j = new Vector(0, 1, 0);
            var k = new Vector(0, 0, 1);

            var p = rotate(i, j, longitudeOfAscendingNode);
            i = p.Item1; j = p.Item2;
            p = rotate(j, k, inclination);
            j = p.Item1;
            p = rotate(i, j, argumentOfPeriapsis);
            i = p.Item1; j = p.Item2;

            var l = semiMajorAxis * ((eccentricity == 1.0) ? 2.0 : (1.0 - eccentricity * eccentricity));
            var c = Math.Cos(trueAnomaly);
            var s = Math.Sin(trueAnomaly);
            var r = l / (1.0 + eccentricity * c);
            var rprime = s * r * r / l;
            var position = mulAdd(i, c, j, s) * r;
            var speed = mulAdd(i, rprime * c - r * s, j, rprime * s + r * c);
            speed /= speed.Abs();
            speed *= Math.Sqrt(2.0 / r - 1.0 / semiMajorAxis);

            return new Tuple<Vector, Vector>(position, speed);
        }

        static void Main(string[] args) {
            var res = OrbitalStateVectors(1.0, 0.1, 0.0, 355.0 / (113.0 * 6.0), 0.0, 0.0);
            Console.WriteLine("Position : {0}", res.Item1);
            Console.WriteLine("Speed    : {0}", res.Item2);
        }
    }
}

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)
}