/// <summary>
        /// Calculates sum.
        /// </summary>
        /// <param name="addend">Addend value.</param>
        /// <returns>Sum.</returns>
        public Vector Sum(double addend)
        {
            Vector result = this;

            result.I = result.SumInI(addend);
            result.J = result.SumInJ(addend);
            result.K = result.SumInK(addend);

            return(result);
        }