\sumThe summation operator, denoted by \sum, is used to represent the sum of a sequence of terms. It is typically used in mathematics to denote the addition of a series of numbers, often expressed with an index that varies over a specified range.
Sum of the first n natural numbers
\sum_{i=1}^{n} i = \frac{n(n+1)}{2}Sum of an infinite geometric series
\sum_{k=0}^{\infty} \frac{1}{2^k} = 2Dot product of two vectors
\sum_{j=1}^{m} a_j b_j