Summation

Summation

File:Greek uc sigma.svg

The Greek letter Sigma (_) is used to denote summation.

In mathematics, summation is the addition of a sequence of numbers; the result is their sum or total. The numbers to be summed may be integers, rational numbers, real numbers, or complex numbers. Summation is denoted by the symbol _ (the Greek capital letter sigma). This symbol is used to represent the sum of a sequence of terms, typically expressed as:

\[ \sum_{i=1}^{n} a_i = a_1 + a_2 + \cdots + a_n \]

where \(a_i\) represents each term in the sequence, and \(n\) is the number of terms.

Notation

The summation symbol _ is used in conjunction with an index of summation, which is a variable that represents each term in the sequence. The index of summation is typically written below the summation symbol, and the upper limit of summation is written above the symbol. For example:

\[ \sum_{i=1}^{n} i = 1 + 2 + 3 + \cdots + n \]

This notation indicates that the sum of the integers from 1 to \(n\) is to be calculated.

Properties

Summation has several important properties that make it a fundamental operation in mathematics:

• Linearity: The sum of a linear combination of sequences is the linear combination of the sums of the sequences. Formally, for any sequences \(a_i\) and \(b_i\), and any scalars \(c\) and \(d\):

 \[
 \sum_{i=1}^{n} (c a_i + d b_i) = c \sum_{i=1}^{n} a_i + d \sum_{i=1}^{n} b_i
 \]

• Commutativity: The order of summation does not affect the result. If \(a_i\) is a sequence, then:

 \[
 \sum_{i=1}^{n} a_i = \sum_{i=\text{any permutation of } 1, 2, \ldots, n} a_i
 \]

• Associativity: The way in which terms are grouped does not affect the sum. For example:

 \[
 (a_1 + a_2) + a_3 = a_1 + (a_2 + a_3)
 \]

Applications

Summation is used extensively in various fields of mathematics and applied sciences. Some common applications include:

• Statistics: Summation is used to calculate measures such as the mean, variance, and standard deviation of a data set.
• Calculus: In calculus, summation is used in the definition of integrals and in the computation of series.
• Physics: Summation is used to calculate quantities such as total energy, momentum, and force in physical systems.

Related pages

• Integral
• Series (mathematics)
• Arithmetic
• Sigma notation