The sum notation uses the capital Greek letter sigma as follows:
Thus if x1 = 6, x2 = 7 and x3 = -2, then
Note that index i can be replaced by any other index and the results will be the same. Thus,
Also the initial value doesn’t have to be 1. For example, assuming k ≤ n
The initial value can also be – and/or the final value can be +.
We can iterate the use of the sigma notation. For example,
We can also use abbreviated notations such as the following:
There is a similar notation for products using the capital Greek letter pi: