One special case of iteration is the algebraic sum. The Summation function requires three arguments. The first argument is evaluated before the summation begins. It's generally used to initialize a counter or index variable. The second argument specifies a limit for the counter or index. And the third argument is the quantity to be added to the sum. For example, calling the Summation function with the first argument assigning to i, the second argument of and the third argument of i returns the sum of all the integers from to So this is equivalent to a For loop that initializes i to runs as long as i is less than or equal to and increases i by each step, while the body of the for loop would increase the variable s by the value of i at each step.
