public static SimpleMatrix Link(SimpleMatrix vector1, SimpleMatrix vector2)
        {
            // check is vector
            if (vector1.Column != 1 || vector2.Column != 1)
            {
                return(null);
            }

            var newRow = vector1.Row + vector2.Row;
            var result = new SimpleMatrix(newRow, 1);

            for (var i = 0; i < vector1.Row; i++)
            {
                result[i, 0] = vector1[i, 0];
            }

            for (var i = 0; i < vector2.Row; i++)
            {
                result[vector1.Row + i, 0] = vector2[i, 0];
            }

            return(result);
        }