Econometric Theory/Summation and Product Operators

To sum a series of variables , the Greek capital letter sigma Σ is used: . There are some properties concerning the summation operator Σ: 1. , where k is a constant. 2. , where k is a constant. 3. , where a and b are constants. This is a result of rules 1 and 2 above. 4. , The double summation operator is used to sum up twice for the same variable: The double summation operator has the following properties: 1. . The order of the summation signs is interchangeable. 2. . 3. . 4. . Finally, the product operator Π is defined as: . Bibliography Gujarati D.N. 2003 Basic Econometrics, International Edition - 4th ed. McGraw-Hill Higher Education 0-07-112342-3 869–870