Question

is double sum defined as ∑∑ a(i,j) = ∑ (∑a(i,j))

Answer 1

Yep, but since addition is associative and commutative you can interchange summing on i or j if you want.

Answer 2

huhm... ok. If we have ∑ a(i), what is a(i) called?

Answer 3

It's a term in the summation, it's essentially a function of i, so for example:

\[\sum_{i=1}^3 a_i = a_1+a_2+a_3\]

Suppose that \(a_i = 7i^2\) then we could write:

\[\sum_{i=1}^3 7i^2 = 7*1^2+7*2^2+7*3^2=98\]

Answer 4

It's called the "summand" honey

Answer 5

cool